I recommend you find someone local (within your state) who restores old machines. They're usually the best ones to buy from. Plus, they usually service the machines afterward for a reasonable price. That's how I got my 3 vintage machines and he services my 'modern' (1973) Viking.
You're probably asking, ok, how do I find such a person? You can go to the antique stores. They always know the collectors, who repairs them, etc. Also, go to the craft shows, especially the quilting ones. That's how I found my local person. He gets old machines, fixes them up and then resells them. Good luck!