It's hard to get anything but a more-or-less pitbull from a shelter anyway - the 'breed rescue' groups run around scooping up all the dogs that appear to be their breed, so there's nothing left BUT pits.
I'm on one breed-rescue email list, and they occasionally send emails asking someone to go to a shelter and pretend to be a regular adopter, then hand the dog over to the breed rescue, because the shelter won't adopt to a group.
I am involved with cocker rescue and shelters call us all the time to come get pure or mixed cockers that they have.