Hornady, Nosler, and Winchester make 8mm Mauser (8x57mm) ammunition. Good USA hunting ammunition can be difficult to find sometimes but it is out there.
The most common (inexpensive) modification of the 8mm Mauser in the USA is almost certainly simply reaming the chamber to 8mm-06. The 8mm-06 ammo can easily be made from 30-06 brass if your friend is a handloader.
A gunsmith would have to check the diameter of the barrel to make sure it really measures .323" and if the action was in good enough condition for the additional power.