There used to be a guy in south Minneapolis who worked on shutters, lenses, machined lens boards, etc, but I don't recall his name, or know if he's still in business. He worked out of his home in the mid-80's. You might ask around at studios. I only needed him once for a minor item.
There also used to be an independent repair shop in downtown Mpls that was factory authorized for almost any brand, and should be able to help you. Sorry, don't recall that name either... looked it up... Marquette Camera Repair, which used to be downtown Mpls on Marquette, but has apparently moved.
Ask at West Photo or National Camera Exchange if you can't get a line otherwise. The people who've been at either place for a while might be able to help.