'71 Duster gas cap question

I'm running into the same dilemma. In the above pic the '71 cap is what I had back in the day before I left it on the trunk and drove off (1997). I have yet to find one that fits the same and locks in place when you turn it. Only ones that fit just keep spinning although they do get "snug" and that's when i quit turning it. Any luck on finding a good replacement that actually works??