Due to the silly gun laws here, there are not a stock item. IIRC, only Scatter Gun Tech is carrying a short barrel as a catalog item. The rest are cut down to order.
I have fired a very short SG in my youth. I was not impressed. Muzzle flash, noise and muzzle blast were increased with few (if any) advantages. I guess it's like a PG shotgun. If you have the need for that configuration (storage), practice requirements increase greatly.
Giz
