I have a threaded 9x21 barrel with a compensator and recoil rod that I will sell. It has never been installed. PM if interested.
You know, it occurred to me after I posted that you probably are not thinking 9x25 Mauser, but rather 9x25 Dillon, which is based on the 10mm Auto case. The pressure for the Dillon wildcat and the 9x21 are close, about 2K PSI apart. However, if you ream the chamber for the wildcat, I do not think the barrel I have would be safe, as you are thinning the chamber walls considerably.
You may be better off starting with a 38 Super barrel and cleaning it up with a 9x23 reamer. The pressures are higher for the 9x23, but the brass is much stronger and you do not lose much metal around the chamber.