It seems to me that I've seen 3" 28 gauge chambers mentioned in a shotgun catalogue somewhere, but 28 gauge shells are all only 2 3/4" long. I checked out a Ruger Red Label 28 with 28" barrels and the straight grip stock. It fit just right and balanced well. If I buy a 28 gauge that would be the one.

I don't think anyone makes a 3" 28 ga; it would be a waste of time anyway IMHO. I believe Beretta now has a small frame 28 but expect it to cost over 2k. There are some small frame sxs 28's out there but they tend to be a bit pricy. In my experience 3/4 oz of shot in a 28 seems to perform way beyond what it should.
C.G.B.