The folks around here are more into emulation of old games running on personal computers and although there are some collectors that may come to the Retrogames site, the forums are not very active these days.

Try here the page looks a little old but check out the links.
http://www.basementarcade.com/index.html
I think there is a collectors IRC channel linked there and also site links for various collectors, repair, parts and manuals.

There are also the newsgroups rec.games.video.arcade that are accessible through Google Groups or a news server with a client.

HTH

UncleVom