Parts can be got or made, seals are pretty standard O-rings and one quad seal.
Don't chintz out on the quad seal like the guy in that blog, you can get them from pretty much any bearing and seal place, they are a minor PITA to change out, and cheap, so get several. IIRC, I paid around 40 cents each.
Have seen guys use the olives from compression pipe fittings for replacements for the transfer seal between the breech and the main body. YMMV.
Easy units to work on, better built that most stuff that you can buy now. Worth fixing, IMO.
Cheers
Trev