Rubber Seal in Trunk for Fuel Filler Neck

I am looking for the rubber seal that goes inside the trunk (on the trunk floor) where the fuel filler neck passes through the trunk floor and then joins the fuel tank. It is a fairly large seal, oval in shape, that screws into the floor with 4 or 6 screws (I forget). This is for my 69 Dart. If you have one or know an aftermarket source that reproduces this seal, please let me know. Thanks.