Having trouble finding a gas cap for my 66 Dart

Hello ,I make these in my shop . I use an O-ring for no leaks whatsoever .I have sold alot of these to members all over the world .

Thanks,

Steve

http://www.ebay.com/itm/270852232382?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649