Caesar Guerini makes the Summit Sporting 20 gauge in 30" and 32" versions. Beretta makes SPII sporting clays guns with 30" barrels in 20 gauge and 28 gauge. I think Perazzi has some even longer barrels (34") for 28 gauge and possibly 20 gauge. A check of the Rizzini's will probably find 30" in 20 gauge. SigArms TT 25 was made in 30", if I recall (probably a Rizzini).

30" 20 gauge can be light and smooth. Pumps and auto's will have the same overall length with a 28" barrel.