RJ,my HD 870 has an 18" and a skosh bbl. My deer 870 has a 20" rifle sighted bbl.it serves as backup outside the shotgun season. Both are set up alike with mag extensions and so on. Even in tight quarters, I feel no difference in handling.For that matter, the bird 870 with its 21" bbl handles like a riot gun.
Don't know about on line, but most gun shops that handle police turnins have a riot bbl or two lying around.