jonm
You might try a guy in Omaha named Ron Miller. Phone: 402 393-4536.
Ron chambers and threads raw factory barrel blanks into 6mm PPC. [6mm PPC shooters support their sport by the money they save on targets. They just shoot through the same hole, over and over and over.]
Ron lives over by Canfields. Has a full machine shop. Very approachable individual and a real craftsman at what he does.
Either he will do the work or will know of someone who does.