I have found "Atlanta Stuttgart" is a good source for used parts,if that is what you are looking for. They are good people, located in Canton, Ga. north of Atlanta, their number is 770-720-1110.
Do you feel like your tech made the correct diagnosis? You may want to solicit second opinions. I'm not a tech, so I'm not qualified to help on this. Good luck on getting your car out of the shop, three weeks is a long time.