My wife and I have fostered somewhere around 250 dogs over the years. All house dogs, one, two or three at a time for various local and national organizations. It's a terrific experience and I recommend it. I'll second petfinder.com as a good place to look. You're local vet should also have a list of shelters in your area and possibly a list of pure-breed dog rescue organizations. We did English Setter rescue for a long time (as you might guess by my avatar).
Please don't buy a dog from a store and imagine that you are "rescuing" it. Perhaps you are, but they will make more to replace it. This is what we need to stop.
Also, don't imagine that only muts and problems are left at shelters or at the end of dirt roads. As Eddies example illustrates, that's just not true. Out of the 250 or so dogs we fostered, we only had a couple who we evaluated as a serious problem. One we kept and rehabed -- he's a lover now -- the other was eventually put down, but he had a tough life all around.
If you want a pure-breed dog, they are redily available. Puppies are also available if that's what you want, although I think old dogs are cool and if you want a puppy you may have to wait a while.
There is a hiden network of dog transporters -- which my wife worked on for some time -- who can ship dogs across the US by setting up travel legs, and getting help from truckers etc. Very cool organization.
Anyway, the point is, the dog you want is already alive and well in a shelter somewhere. You just have to find him before his time is up.
Cliff
Old dogs are Cool!