original 70 Challenger locking gas cap

I have an original locking gas cap for my 70 Challenger but do not have a key for it. I took it to a locksmith and I'm told they cannot make a key for it becasue the cylinder is broke. Does anybody know of replacement cylinders for the cap? I can still user it without the key but it would be nice to have in my pocket.

Sorry - I don't know a source, but I think the locking caps were made by Briggs & Strat back in the day if that helps..