There are no barrels other than the 23" Rem Choke Vent rib Special Field barrels available for the Model 870 Special Field.
The Special Field shotgun has a shorter magazine tube than the standard 870. This being the case, the barrel guide ring is brazed to the barrel closer to the chamber.
The guide ring on standard barrels won't reach the magazine tube because of its shorter length. On our site we have a listing of specialty parts dealers that may offer replacement Special Field barrels. Specialty Parts Dealers List