Where are you located (approximately)? There are plenty of machines around - and many more for sale. A local dealer had a full restore (and I mean FULL) on sale for $1800. I wanted it so badly. I know of a few owners in Virginia as well. One guy has the discs sit down cab. It's only in reasonable shape, but it plays great and he's working on it.
You should really come out to www.magfest.org next year. Part of the event is a warehouse-sized arcade open 24/7 and all free play. They had at least two TRON cabs this year and the discs machine as well. Here's some random video of this year's room. http://www.youtube.com/watch?v=T3EfDPBB36o