Contact your closest rescue group and ask them what their policies are about owner turn-ins and adopting to a family that's just returned a dog. Have you taken possession of Oso yet? If not, then I would try to arrange for rotty rescue to take him in to their program, evaluate him and then be first in line to foster or adopt him. That way, you aren't tagged as being a "returner." They may also be more likely to take him in to their program if there's already a foster home lined up, since space is often the #1 reason a dog can't be taken in by a rescue. Be aware you will probably go through a screening process and maybe a home visit to be a foster home.
If the dog has a bite history, you'll need to ask what the rescue's policy is on taking biters as well.
As for how to go about contacting them...an email is a good start. Here's a few in NC
http://ncrottierescue.net/ http://www.ssrr.org/
Good luck!