Go to Midway, or CheaperThanDirt, or Brownells and search for a stock. Pick one you like.
For defense shotguns, most people run them too long. So I suggest a plastic stock and a KickEze sporting clays grind to fit pad. Cut off some stock, add the pad and countour it with rolled edges all around. Tape and belt sander to make general shape then 400 grit wet paper to smooth. I cut stocks so that there is about 1 to 2 inches between the back of my thumb and nose, or about 3/4 to 1" between the back of the stock and the front of my bicept with finger on the tirgger. You might have to have someone local help you or go look at one of the on-line videos about fitting combat shotgun stocks.