User blog comment:Bluegear93/What if there were no Geth?/@comment-118213-20111023182556/@comment-4069499-20111025201956

There's nothing that says that the geth are the only ones capable of creating prosthetic limbs in the ME universe, Saren just happened to get his from the geth. For all we know, Saren didn't even need a prosthetic and just got one because Sovereign felt it would enhance him in some manner.