I have picked up a few arcades through KSL as well (
http://forum.arcadecontrols.com/index.php?topic=74490.0 being my latest). I agree that KSL does seem to have more deals more often on arcades, but I have still found some listed through craigslist that didn't make it to KSL (I used
http://crazedlist.org/ to search all the utah areas at once).
I have also had some luck with my local arcade (Fun Unlimited), the guy who owns it is a real nice guy. He doesn't seem to know what his machines are really worth (in a bad way, his prices are generally too high), but since he's not actively selling them, it doesn't seem to be a problem for him. He was really reasonable when I worked out a trade with him (got my Crystal Castles from him, I love that arcade). He also has some contacts with other operators that may be able to locate a specific game.
I worked with a guy down in ogden (for a trade) that ended up getting a good deal on an empty cab from the nickel cade down there (he got a Virtual Fighter cab that was gutted, and we helped him convert it into a 4 player mame cabinet -
http://forum.arcadecontrols.com/index.php?topic=64354). I think he may have been working with in the past (built up a relationship) but that seems like a prime location to get good deals from (they have pretty high turnover in their arcade, so I'm sure you could get some of the low performers for a steal).
When I started this hobby, I thought it was impossible to find reasonable cabs here in Utah, but now, I don't have room for the ones I have (not sure where I'll put the Star Wars when it's done, but I'm sure I'll find a place

)