Mossberg has brand new, tactical version of the SA-20, with a short barrel, tactical stock with pistol grip. It's not on their website yet as of now but it can be seen in their new catalog/magazine that I've seen for sale on magazine racks.
Weatherby has their new SA-459 in 20 gauge, semi-auto, pistol grip.
http://weatherby.com/product/shotgun...to_tr/sa459_tr