A member of the AC Owner's club has contacted Ceandess (the maker of the original Ace and 260/289 Cobra gas caps) and they are considering making a limited run of caps, depending on interest. Below is the a link to the thread he started if anyone is interested in buying one. I think it is still in the early stages with many details to be worked out, but Ceandess seems to be interested which is a good sign.
Jay
AC Owners Club - New Correct Ace,Aceca & Cobra Fuel Caps