I already own a Win 1200 and I was wondering where I can buy aftermarket parts for this gun like a mag extension and shorter barrel. Thanks Lee
As far as the barrel, I'd just cut down the one you have. Choate makes several different sizes of mag extensions, Tac-Star makes a side saddle (only Tac-Star product I'd use, they're good), and Knoxx makes some replacement stocks.
The Winchester M1200 was supposed to be the replacement for the great Winchester M12. It never came close the reputation the good old reliable M12 had. Like what was said above, cut her down. They aren't worth much in the used market.