Study pictures in catalogs, then make one out of cardboard & duct tape; actually, make several. Fiddle with different shapes & sizes 'till you get it just the way you want it. A lot will depend upon the size of the paw itself. For durability, I'd glue & stitch the hide to leather; both the front and the flap, and I'd stitch a piece of leather onto the back to take an all-leather sporran strap; less wear on the kilt than chain.
You've gotta post pictures of that when you're done!