Groomers if the vet won't work with you. Your vet sued you? Wow, vets should be well aware that they are taking risks with the animals. Mom never got sued with her last cat who we nicknamed "Maggie the mauler" since she scratched a lot and we always knew which cat was screeching as the vet walked back in rubbing the bloody scratches on his hands.
Well I don't really think you should bring him to a vet or a groomer. If I was the dog I would be thinking, someone I don't know and am not sure if I trust is trying to do something that I don't know. If you know how to cut the nails without hurting him I would say get a couple people you know and that the dog knows. You can give him some doggie calm down pills. (we gave our dog that for thunder storms and fireworks.) Hold him down good. If he attempts to bite put a muzzle on him. and have someone that knows him talk to him to calm him down. Things like this are all based on trust. You have to make sure he knows that you wont hurt him.