I believe you mean EJECTOR. Try Numrich, Jack First Gun Parts (So. Dakota), or call Smith and ask then for their recommendations as to where you might try.
S&W did NOT make Shotguns, they simply put their name on them so I would ask who made them and contact that Company if possible. Example: High Standard and Marlin made firearms for Sears so if you had a Sears marked gun you could find parts that were made for the High Standard or Marlin corresponding models and they would fit.