Other than contacting Lucasfilm…
Norman Reynolds is likely your best bet as to someone having an idea where the chair ended up / what happened to it.
Bill Hargreaves would be another to likely know. Maybe George too? Perhaps for his own museum opening soon?
Jedit: I seem to remember there being photo opportunities with the chair at one of the Celebrations - whilst it could have been the real thing - it could also have just been a good replica…