Not BPCR, but I ordered some .475 Turnbull cases from Turnbull, and half of them came primed
I guess I could always make them from 50-110's, or ,348's, but...
I already had a .45-90 on order, and then found a .45-90 High Wall, so I can easily justify a few hundred .45-90 cases. And have so obtained them.
Derby, if you decide to get a rifle, the .45-70 is never a mistake. And remains popular. Brass should usually be available.