Try the gunsmith at A2Z Gunshop in Rush City, MN. He's found some rather unusual parts for me in his back room or has known someone who knew someone that could help. The phone number for him is: 320-358-9999.
Failing that, I would try Superior Shooter's Supply up in Superior, WI. I don't have their number on hand but they have also come up with some things I couldn't find elsewhere.