I wonder if Qual Cart is making much of anything these days.Here's a start on finding brass to reload. Best of luck.
New, unprimed brass. Made in USA. This is not loaded ammunition. Quality Cartridge is a devoted manufacturer of Custom, Obsolete, and Wildcat cartridge cases. They provide premium properly headstamped empty cartridge cases in the widest array of calibers.www.grafs.com
Could you make cases from .264 Win mag brass by setting the shoulder back? You'd need to to move it by about 0.33 inches which could maybe be done in small steps with trimming and maybe fire forming. The .264 Win mag shoulder angle seems favorable for this. Also you'd likely need to trim as you go.