Single wire neutral safety switch

I've searched this forum trying to figure out where I can purchase a single wire safety switch for a 66 Dodge Dart with a 904 Auto transmission but didn't come up with a definitive answer. Does anyone know where I can purchase one? I also noticed some referred to the three wire safety switch and only using the center connection but I was unsure about the rooster comb and which one to use. Any help would be greatly appreciated. Thanks