Stereo King is out. Their Advertising guy said that Hood River Fairground is too far away.
Outrageous Audio is probably out. Their manager said they don't do car shows anymore, but to call the owner tomorrow.
The Sound Choice is a possibility. Rich said he might be interested, but he wanted to research it a bit and sounded pretty suspicious (I suppose I was talking a bit like a salesman). I'll call them back next week.