Yep no problem cutting a shotgun barrel down to 20" or so, I think Brownells has a squaring off tool you can use to polish out the muzzle after it's cut. If you have a vent rib you can just choose a nice spot in the middle of the rib attachment and cut there. If not there are quite a few different options for attaching a front bead.
Or you can just get one, I know wholesale sports used to carry a few random barrel types. I'm sure Cabellas or one of the many sponsors up above will have something. I'd try Wolverine or maybe Calgary shooting centre maybe? Big shops should have lots of oddball parts around.