UM,

If it is truly an older model 20 gauge remington 1100 (built on a 12 gauge frame), then what you are looking for does not exist. If you remove the barrel and a quarter can slip through the barrel ring, then it is the older model 1100, and no-one makes barrels for them. There are usually a few "old style" barrels available on e-bay, but they will be smoothbore, and most will be bird barrels either ribbed or smooth with a bead. I personally purchased a set of Williams Firesights adjustable rifle sights that attach directly to the rib of my bird barrel (skeet choked) and just shoot remington sluggers through it. In my 20 gauge, these are extremely accurate at 50 yards. If you are looking to mount a scope, you'd have to look into a B-Square type mount. Refer to the remington site if need be.

KEJ