Hutch,
You might try Buffalo Arms, they load some custom ammo,or check with other custom handloaders.There is a new(relative term)cartridge made for insert barrels(einstecklauf), known as 6x70R Krieghoff.Huntington Die Specialities, has this brass from time to time.I'm pretty sure this brass will chamber in your rifle, and if so, you could fireform it.Bertram might have formed cases, I don't know.If you get desperate enough to come to Alabama,I will try to help you.
Mike