It's easy to make brass for you 7.65 Argintine rifle.
Simply run .30-06 cases in a 7.65 Argentine full-length sizing die, trim to length, and deburr.
If you want to go cheap, use the Lee dies in this caliber, and the case trimmer w/shell holder and you are all set.
If in good condition, that was a fair price you paid.
Some of those old Mausers are amazingly accurate! It sounds like you have a great shooter!
John