The 8mm Mauser (actually it's the 7.9mm Mauser) is the only ammo that will work.
This is no different than any firearm chambered for a specific cartridge. Only the ammo it's chambered for can be used.
For ammo, there's the commercial made hunting ammo made by most American cartridge companies, ammo made by Norma, and if you can find it, military surplus corrosive primed ammo from any number of companies.
I don't keep up on this, but it's possible Russia or some of the former Commie countries are selling commercial steel cased ammo.
To use surplus corrosive ammo, after shooting just flush the bore and bolt face with hot water, then clean as normal.