Don’t hold your breath on the Sherman. If you think SAUM is hard to find then forget about the Sherman.
ADG, Bertram, and Hornady are all making 6.5/7 SAUM at this point. That would be the way I would lean. Necking up a PRC is also an interesting idea, and should have plenty of components available in the near future. Only issue might be a reamer but Manson or whoever should be able to make one for you.
Other option would always just be to go 6.5 and shoot the heavies. They will border on 7mm performance if not beat it in some aspects. But at that point GAP 4S is your only option as it has a short enough FB without spacing you out of short actions.
ADG, Bertram, and Hornady are all making 6.5/7 SAUM at this point. That would be the way I would lean. Necking up a PRC is also an interesting idea, and should have plenty of components available in the near future. Only issue might be a reamer but Manson or whoever should be able to make one for you.
Other option would always just be to go 6.5 and shoot the heavies. They will border on 7mm performance if not beat it in some aspects. But at that point GAP 4S is your only option as it has a short enough FB without spacing you out of short actions.