MPEX sold those parts to Fred Lustig of Reno, NV years ago. As far as I know Fred is still alive and still repairing cameras. I've seen comments that he's reluctant to sell parts, prefers to do the repairs (which use the parts) himself. Fred doesn't have much of an Internet presence and doesn't publish his e-mail address but he's listed in the Reno telephone directory.
Originally Posted by WetMogwai
Jerry, look up his phone number and call him. Alternatively, look for a parts camera. Whatever you do, be clearer about which model Speed Graphic you have.