They are out of production.  If you can find them, extra connectors  have identical bodies for the male and female side.  So you can stick a pin and a receptacle in the same plastic body.   If you take a cue from the SAE folks and put a receptacle on the hot wire coming from the battery, and a pin to the ground wire, you get a polarized plug.  Unfortunately for polarization, Later Widder products were manufactured with rubber-molded connectors, which cannot be mixed and matched in this way.