I went to Matt Christiano's ranch once. He was one of the organizers of pin a go go, but I believe Brad Grant is now the head guy.
He had about 200-300 games that were set up and playable. Not all in top notch shape but very few with problems that made them unplayable. He also had a warehouse of games to be fixed/restored that looked like that ending scene in Raiders of the Lost Ark. It looked like at least 500 games in there.
Richard Conger has something like 1000 games. He focuses on EMs and likes pre-flipper games. He brings some to local shows. I'm not too big on the game play but they are really beautiful machines. Some of them have surprisingly deep rules, and when you consider there was no cpu keeping track of everything, it's quite impressive.
The place I visit fairly often is the PPM warehouse. There are around 500 games in there, and they received the gordon hasse collection, so I think there are a lot more than that. Most are in playable condition but maybe a dozen are set up at any one time. They rotate them into the museum and bring them to pacific pinball exposition and other shows.