I think the inlet is .BS standard and outlet NPT. I just calculated if i were to build the pressure regulator with desired parts, it will cost $600 and the cheapest is $ 450. Similar to GLA ultimate pricing.
"Regulator bullnose stems can become damaged over time from general wear and tear incurred when changing bottles. This damage can cause leaks at the cylinder connection, so bullnose stems and / or regulator nuts are often replaced. Our bullnose stems are available in 3 regulator thread sizes to suit different popular regulator manufacturers
is it the right answer? good luck on the regulator, if you know any research facility or hospital facility station engineers, talk to them, they may have a couple spare double stage regulators in good price.
just avoid the used oxygen service regulators.