Okay, here's the deal. A local bowling alley here in College Station, TX had a bunch of stuff up for auction. Apparently they had either closed another alley in another town or they just accumulated this stuff over the years. They had everything from old drink coolers to ice cream dispensers to my Tron.
I have found that things like this are a decent source as long as you aren't in a hurry to find a cab. I've seen two cabs in the last couple of years that were just being thrown out. Keep your eyes peeled for businesses closing down or new businesses going into existing store fronts. Sometimes those old store fronts will have "junk" left behind in them, and when the new business goes in, they throw it out or sell it cheap.
Just three weeks ago an old Montgomery Ward here was being demolished, and they were throwing out a two player side by side driving cab complete with steering wheels, shifters, and pedals. It sat out there for several days before somebody picked it up. I had no interest in it, or I would have picked it up myself. Heck, if I would have had time, I would have just parted it out on the spot and sold the controls.
The key to finding stuff like this is to let all of your friends and acquaintences know you are looking for old arcade machines. That way when someone runs across one, they'll think of you.