Brownells has 8lb of varget and cci 450 primers in stock now but they are mighty proud of them, with the 8lber and two cci450s and coupon code "jan60" the total comes to 667.
Its pretty darn pricey but its there now to be had if you are willing. It comes out to about the same as if you buy single pounders though so it can be "justified"
A powder thats good for a 308 175gr bullet will be about right in burn rate for a 6br 105.
Do some skimming through here and see whats being used
https://www.snipershide.com/shooting/threads/6mm-br.6895954/