If your vet doesn't have the technology to scan Buddy for a microchip perhaps your county or city animal shelter has it. I have a friend who managed to fall in love with a foundling and waited for more than a month to do that and sure enough, found the bereaved owners. Both of my brats have them, one in the ear and the other, a foundling, has one between his shoulders that I had placed there. I also have my name and phone # on metal plates riveted to their collars.
In any case, good luck in your endeavors finding the owners or keeping him. I know I could never foster dogs; I'd end up with ten of them because I couldn't part with them.