I did some more determined research on early silencers and got lucky right away with this piece on Maxim silencers:

https://www.forgottenweapons.com/i-found-this-old-maxim-silencer/

and also this sales brochure:

https://www.forgottenweapons.com/accessories/maxim-silencer/

(see the pdf download link in the middle of the webpage)

Apparently these silencers were patented in 1909 and offered by mail order houses through 1934. Then the government imposed a $200 stamp duty. This killed sales as no one was willing or able pay a $200 tax to silence a $15 rifle, particularly in the Great Depression.

The coupling for these silencers appears to be the same as the one mounted on my 1912. See the drawing at the top of page 2 of the sales brochure.

Unfortunately it is illegal today to possess a Maxim silencer unless it was registered with ATF (or its predecessor) when originally acquired. You can not buy an old one and register it. Therefore the only hope is to find one that comes with registration paperwork and the original $200 stamp. There are probably some out there, but it must be one of the rarest accessories to find.