They use this cast list taken from Wikipedia http://en.wikipedia.org/wiki/List_of_Harry_Potter_cast_members

Here are their lists

http://theatre.revstan.com/2011/07/why-harry-potter-reignited-my-love-of-the-...

http://earlhamstreetgutter.blogspot.com/2011/07/harry-potter-cast-members-see...

@nick370 has added his list to the mix http://nick730.blogspot.co.uk/2013/03/potter-spotter.html#more

And here is mine.

01 - Harry Potter - Daniel Radcliffe - Equus — Gielgud Theatre (2007)
02 - Ron Weasley - Rupert Grint - Mojo — Harold Pinter Theatre (2013)
03 - Charity Burbage - Carolyn Pickles - Fram — Olivier Theatre (2008)
04 - Armando Dippet - Alfred Burke - A Midsummer Night's Dream — Barbican Theatre (1995)
05 - Albus Dumbledore - Richard Harris - Henry IV — Wyndhams Theatre (1990)
06 - Albus Dumbledore - Michael Gambon - Mountain Language — Lyttelton Theatre (1988)
07 - Argus Filch - David Bradley - King Lear — Lyttelton Theatre (1990)
08 - Filius Flitwick - Warwick Davis - See How They Run — Richmond Theatre (2014)
09 - Rolanda Hooch - Zoë Wanamaker - Othello — Young Vic (1989)
10 - Gilderoy Lockhart - Kenneth Branagh - Hamlet — Barbican Theatre (1992)
11 - Minerva McGonagall - Maggie Smith - Three Tall Women — Wyndhams Theatre (1995)
12 - Irma Pince - Sally Mortemore - The Lady of Pleasure — White Bear (2011)

13 - Poppy Pomfrey - Gemma Jones - Battle Royal — Lyttelton Theatre (1999)
14 - Quirinus Quirrell - Ian Hart - The Homecoming — Comedy Theatre (2001)
15 - Horace Slughorn - Jim Broadbent - The Recruiting Officer — Royal Court (1988)
16 - Severus Snape - Alan Rickman - Antony and Cleopatra — Olivier Theatre (1998)
17 - Pomona Sprout - Miriam Margolyes - Dickens' Women — Hampstead Theatre (1991)
18 - Sybill Trelawney - Emma Thompson - Look Back In Anger — London Coliseum (1989)
19 - Katie Bell - Georgina Leonidas - Agatha Christie's Black Coffee — Richmond Theatre (2014)
20 - Lavender Brown - Jessie Cave - Arcadia — Duke of York's Theatre (2009)
21 - Cho Chang - Katie Leung - The World of Extreme Happiness — The Shed, National Theatre (2013)
22 - Colin Creevey - Hugh Mitchell - Arcadia — Duke of York's Theatre (2009)
23 - Roger Davies - Henry Lloyd-Hughes - Posh — Royal Court Theatre (2010)
24 - Leanne - Isabella Laughland - Greenland — Lyttelton Theatre (2011)
25 - Neville Longbottom - Matthew Lewis - Our Boys — Duchess Theatre (2012)
26 - Luna Lovegood - Evanna Lynch - Disco Pigs — Trafalgar Studio 2 (2017)
27 - Pansy Parkinson - Genevieve Gaunt - French Without Tears — Orange Tree Theatre (2015)
28 - Dean Thomas - Alfred Enoch - Antigone — Olivier Theatre (2012)
29 - Ginny Weasley - Bonnie Wright - The Moment of Truth — The Large, Southwark Playhouse (2013)
30 - Oliver Wood - Sean Biggerstaff - Girl with Red Hair — Hampstead Theatre (2005)
31 - Dedalus Diggle - David Brett - Outward Bound — Finborough Theatre (2012)
32 - Elphias Doge - David Ryall - The Changeling — Lyttelton Theatre (1988)
33 - Aberforth Dumbledore - Ciarán Hinds - Simpatico — Royal Court (1995)
34 - Arabella Figg - Kathryn Hunter - Our Country's Good — Royal Court (1989)
35 - Remus Lupin - David Thewlis - Icecream — Royal Court (1989)
36 - Alastor Moody - Brendan Gleeson - Saint Oscar — Hampstead Theatre (1990)
37 - James Potter - Adrian Rawlins - Three Sisters — The Queens Theatre (1990)
38 - James Potter(y) - Robbie Jarvis - Shivered — Southwark Playhouse (2012)
39 - Lily Potter - Geraldine Somerville - A Jamaican Airman Forsees His Death — Royal Court Theatre Upstairs (1991)
40 - Kingsley Shacklebolt - George Harris - Mountain Language — Lyttelton Theatre (1988)
41 - Nymphadora Tonks - Natalia Tena - The Clean House — Richmond Theatre (2008)
42 - Arthur Weasley - Mark Williams - Toast — Royal Court Theatre Upstairs (1999)
43 - Bill Weasley - Domhnall Gleeson - Now or Later — Royal Court (2008)
44 - Molly Weasley - Julie Walters - All My Sons — Cottesloe Theatre (2000)
45 - Lord Voldemort(y) - Richard Bremmer - The Good Person of Sichuan — Olivier Theatre (1989)
46 - Lord Voldemort(y) - Christian Coulson - Journeys End — Comedy Theatre (2004)
47 - Lord Voldemort - Ralph Fiennes - King Lear — Barbican Theatre (1991)
48 - Alecto Carrow - Suzie Toase - One Man, Two Guvnors — Lyttelton Theatre (2011)
49 - Amycus Carrow - Ralph Ineson - Hangmen — Royal Court Theatre (2015)
50 - Barty Crouch Jr - David Tennant - What the Butler saw — Lyttelton Theatre (1995)
51 - Lucius Malfoy - Jason Isaacs - The Force of Change — Royal Court Theatre Upstairs (2000)
52 - Narcissa Malfoy - Helen McCrory - Macbeth — Riverside Studios (1990)
53 - Peter Pettigrew - Timothy Spall - The Caretaker — Old Vic (2016)
54 - Scabior - Nick Moran - Real Classy Affair — Royal Court Theatre Upstairs (1998)
55 - Amelia Bones - Sian Thomas - The Illusion — The Old Vic (1990)
56 - Mary Cattermole - Kate Fleetwood - The Tempest — Shakespeare's Globe Theatre (2000)
57 - Reg Cattermole - Steffan Rhodri - The Tempest — Shakespeare's Globe Theatre (2000)
58 - Barty Crouch Sr - Roger Lloyd Pack - When We Are Married — Savoy Theatre (1996)
59 - John Dawlish - Richard Leaf - Not about Nightingales — Cottesloe Theatre (1998)
60 - Amos Diggory - Jeff Rawle - Noises Off — Lyttelton Theatre (2000)
61 - Cornelius Fudge - Robert Hardy - The Audience — Gielgud Theatre (2013)
62 - Mafalda Hopkirk(v) - Jessica Hynes - The Night Heron — Royal Court (2002)
63 - Mafalda Hopkirk - Sophie Thompson - Clybourne Park — Royal Court Theatre (2010)
64 - Rufus Scrimgeour - Bill Nighy - Betrayal — Almeida Theatre (1991)
65 - Pius Thicknesse - Guy Henry - The Changeling — Lyttelton Theatre (1988)
66 - Dolores Umbridge - Imelda Staunton - Bold Girls — Hampstead Theatre (1991)
67 - Frank Bryce - Eric Sykes - The School for Wives — Piccadily Theatre (1997)
68 - Mrs. Cole - Amelda Brown - My Heart's a Suitcase — Royal Court (1990)
69 - Dudley Dursley - Harry Melling - The School for Scandal — Barbican Theatre (2011)
70 - Marge Dursley - Pam Ferris - Apples — Royal Court (1989)
71 - Petunia Dursley - Fiona Shaw - The Taming of the Shrew — Barbican Theatre (1988)
72 - Vernon Dursley - Richard Griffiths - Heartbreak House — Almeida Theatre (1997)
73 - Mr. Granger - Ian Kelly - A Busy Day — Lyric Theatre (2000)
74 - Mrs. Granger - Michelle Fairley - Factory Girls — Tricycle Theatre (1990)
75 - Mr. Mason - Jim Norton - The Weir — Royal Court (1998)
76 - Mrs. Mason - Veronica Clifford - Coventry Carol — Hampstead Theatre (1995)
77 - Gellert Grindelwald - Michael Byrne - Death and the Maiden — Royal Court Theatre Upstairs (1991)
78 - Olympe Maxime - Frances de la Tour - Blinded by the Sun — Cottesloe Theatre (1996)
79 - Everard - Sam Beazley - King Lear — Lyttelton Theatre (1990)
80 - The Fat Lady - Dawn French - When We Are Married — Savoy Theatre (1996)
81 - The Grey Lady - Kelly Macdonald - Hurlyburly — The Old Vic (1997)
82 - Moaning Myrtle - Shirley Henderson - Mill on the Floss — Tricycle Theatre (1994)
83 - Phineas Nigellus Black - John Atterbury - Ivanov — Wyndhams Theatre (2008)
84 - Sorting Hat(v) - Leslie Phillips - The Merry Wives of Windsor — Barbican Theatre (1997)
85 - Food Trolley Lady - Margery Mason - Three Sisters — The Playhouse Theatre (2003)
86 - Xenophilius Lovegood - Rhys Ifans - Volpone — Olivier Theatre (1995)
87 - Mr Ollivander - John Hurt - Krapp's Last Tape — Ambassadors Theatre (2000)
88 - Ernie Prang - Jimmy Gardner - A Midsummer Night's Dream — Barbican Theatre (1989)
89 - Madam Rosmerta - Julie Christie - Old Times — Wyndhams Theatre (1995)
90 - Stan Shunpike - Lee Ingleby - Cressida — Albery Theatre (2000)
91 - Rita Skeeter - Miranda Richardson - Mountain Language — Lyttelton Theatre (1988)
92 - Tom the barman - Derek Deadman - A Midsummer Night's Dream — Almeida Theatre (1996)
93 - Eldred Worple - Paul Ritter - The White Devil — The Pit (1996)
94 - Aragog(v) - Julian Glover - Julius Caesar — Barbican Theatre (1996)
95 - Dobby(v) - Toby Jones - King Lear — Hackney Empire (1995)
96 - Firenze(v) - Ray Fearon - The Merchant of Venice — Barbican Theatre (1994)
97 - Grawp - Tony Maudsley - The Anniversary — Garrick Theatre (2005)
98 - Griphook - Warwick Davis - See How They Run — Richmond Theatre (2014)
99 - Kreacher(v) - Timothy Bateson - Absolutely! (Perhaps) — Wyndhams Theatre (2003)
100 - Kreacher(v) - Simon McBurney - The Caucasian Chalk Circle — Olivier Theatre (1997)
101 - Magorian - Michael Wildman - The Darker Face of the Earth — Cottesloe Theatre (1999)
102 - Shrunken Head(v) - Lenny Henry - Othello — Rose Theatre Kingston (2009)

It isn't complete though