Where is all the brass???

Not that it's much easier to find, but 270wsm and 300 wsm can both be used to form 7wsm.

Just FLS the 270 or 300 in a 7wsm die. You'll be creating a false shoulder to HS on. Just carefully set the die so cases have a mild "crush fit" in the chamber.

Case capacity on first loading will be slightly less, so charge accordingly.