dmorgan - I just spoke on the phone with Marc at Sun Valley. They do not sell parts; however, he did give me the name of EVT Parts in Los Angeles where they do sell transmission parts. The phone number for EVT is: (310) 327-2910. Their website is:
EVTParts.com

Marc also said you will need the casting number for the part you are seeking. Sometimes the casting number is different from the Mercedes part number.