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Maybe you could push some 300 prc brass through the blaser die, trim and neck turn and be good to go?
A long and fastidious process.

My bad , I felt to properly read the beginning where he has already the rifle in that caliber.
28 nosler could be the next approach

At that price from brass, I would get it chambered in 7rm and carry on till 7 prc becomes popular enough that components and ammo are in most local shops. Then consider rechambering or rebarreling...