So, interesting follow up to this 5+ years later...
I recently contacted Bushy for help with a Windham ACR stove-piping M193 ammo. I'd read on here that the H/L regulator was developed and used to fix this exact issue. I started by calling the parts department and ordering one -- no surprise: the parts guy didn't even know about them. I figured it was a "service department only" secret kinda thing and asked to be transferred. Turns out part and service are the same thing - he was also the guy that would get and fix my rifle if I sent it in. So we chatted for a while. There's only one guy that's been there longer than him, so he asked his senior. He hadn't heard of it either. So I directed him to the forums (the primary thread on the issue, which I can't seem to find now), which he read, and he'd never even heard of such a thing. After more discussion he gave a last ditch effort by putting me on hold and talking to the military division...
A short while later, he had the answer: they exist after all but are military-only, no exceptions. Absolutely no way to get one, even if you sent in a rifle that needed it. His official recommendation to fix the rifle in question is to avoid m193 ammo, which isn't the best answer but it's fair.
Just thought I'd pass that along.