Proof Research makes them. Got mine back from Vestal's a couple weeks ago.
May try to contact hells canyon armory (mike Johnson) and ask.
This is what I would do. Talk to mike about what you're building/thinking.
Bummer... recently? I saw he got a new wrapping machine, didn't know if the restriction was cutting or wrapping
Nice weapon, how is the recoil on it with that light barrel? Is that a 375 Cheytac?