For what its worth I ride a board 260mm wide on 10.5 boots, I think you may need wider than 272mm for your hoofs. Also a bigger side cut radius will get you a wider board in the middle without being overly wide at the tips.
Donek order custom snowboards alternative to Burton Custom x snowboard K2
these guys will do anything you want
Prior Snowboards and Skis
these guys can do upto 28.5