Compass Lake Engineering @ 719 White Drive, Alford, FL 32420 w/ph: 904-579-1208.
Accuracy International, P.O. Box 2019, Bozeman, MT 59715 (406) 587-7922.
JP Enterprises, P.O. Box 26324, Shoreview, MN 55126, (612) 486-9064.
Bill Wylde, Greenup, IL, (217) 923-3266.
Never used any of the four. All were mentioned by Feamster in his book, Black Magic. Heard about them from other sources (Precision Shooter or American Rifleman).