Is there any way you could buy some time?
If you had a little more time to rehome him, you could make up some flyers and post them in local vet offices and pet stores, and also try checking with your vet to see if they know of any clients who are wanting another dog. Probably unlikely, but it would be worth a try.
You might also check out some local rescues (you can find them through Petfinder's website)...there is a slim chance you might be able to get one of them to take him, and again, it at least wouldn't hurt to try. His age and all you have done for him are in his favor.
Good luck, I hope something works out for you.