To everyone looking for games, distributors and operators are the wrong places to look. Most of them don't have crap anymore. The places to get them are other collectors, classified advertisements, auctions, game resellers, and people you already know.
For other collectors look on rgvac, klov.com, and here (in that order). Use google to search RGVAC for the name of your city or state, then contact posters who live in your area to see if they have anything or know anyone who does.
Check the local classified ads everyday. Games usually pop up pretty regularly.
Not every place gets arcade auctions, but many places do. So go if you can.
To locate game resellers search ebay for local games, and see if anyone in your area is selling more than one. Contact the people who have multiple games for sale, and see what else they have. Those guys usually have tons of stuff, and often don't want to deal with dead conversions because they aren't worth the labor involved in fixing them. Dead conversions are perfect for Mame.
Also tell everyone you know that you are looking for games. Most people don't have any, but many of them know someone who does. If you tell enough people you will find one.
Also, don't forget to simply search ebay, sometimes things do go for reasonable prices there.
Here is the real numbers as to where Dave and I have picked stuff up. I probably forgot a few, but you get the idea.
Operators/Distributors - ZERO games
Word of mouth - 10 games
Ebay - 4 games
Classified ads - 7 games
Auctions - 9 games
OTHER COLLECTORS - 15 games (4 more on the way)
Left for dead - 1 game
Everyone trys to call operators, they are pretty much running dry as a source. I only know one guy who ever has any luck with this, and he brings a big wad of cash with him and always pulls out multiple games (but it always seems to be from former ops, not current ones). But even he says that scene has almost dried up. People have been doing that for like 15 years now, there really isn't much left.