Was able to machine one from a piece of brass stock. Fabbed a male thread to verify count and pitch accuracy. Was able to also put the knurl in the cap edge (the math to get the knurls to mate up was interesting).
We ended up with an exact copy of the original...now I just need 100 years of patina to set in and you'll never know the difference.
We can now make them upon request but be advised it won't be cheap. It will cost ~$250 usd for us to make one. I'll post a picture up when I get a chance...