PWM- if this brass is the same as 6.5 and 8X68, it is fairly easy to get, but expensive. I noticed you mentioned use of magnum ctg. cases. The 6.5x68mm Sheuler case I am familiar with has a .522" head dia. I merely turned the belts on .375H&H brass down to .522" so they'd fit perfectly in the 6.5X68 as well as a 9.5X68 I thought of and chambered up 10 years ago.
: I found WW brass to be about the best, with the highest capacity of the American makes.