Oh, and I meant to add, it turns out that the vet *had* scanned him for an AVID chip...I just didn't realize it. The first time they scanned him, it apparently said something about a "possibility of an encrypted chip," but then they scanned him again for an AVID chip and it said "chip not found." I called today to make sure, before taking him somewhere else to be re-scanned.
Also, it is interesting how things work out sometimes. A lady involved in rescue happened to have stopped in at the vet office for something yesterday, right around the time we brought him in to be scanned. She was so upset at his appearance, that she told us later she actually cried after leaving the vet. Anyway, she called us today to let us know that she had found him a foster home. I know we haven't given it very much time to find his owners, so I am not sure if sending him into rescue is the right thing to do or not...but it's not really feasible to keep him very long, either.
In any case, it's always good to have options.