I don't know if you get an answer about that rig.
Many years ago, and after watching the movie "Exposure" (also known as "High Art") with Peter Coyote, I contact Gary Randall in order to ask him where I could get a leather shoulder sheath. He send me the address and phone of Greg Gutcher, from Sullivans. I contact Greg and he made me one of those for a standard 8" #1. Some time after that I began making leather sheaths for me and for some friends and I was able to make a leather shoulder sheath, but changing the original design. Instead of carrying the knife below the left arm, I made the rig so you can carry the knife below the right arms, knowing I am a right handed. So you could still carry a gun on your left side.

Buy the way, this is my #1 and the sheath I made. (the skull is a plastic model for schools)