Restorationspecialities.com Auveco pn 5206 tubular speed nut will work $0.40
A very nice company I had a chance to visit and get a tour from the owners. They work with customers to reproduce parts (rubber, metal, fasteners) using existing (i.e. used) components. For example, they had a customer who wanted a Toyota window rubber gasket that was no longer available. Using what was left of the gasket and using 3D precise measurements, they worked with the customer until they had a precise duplicate of the original before selling it to the customer. They often make several of that part, and put it on the shelf for future customers.
When I inquired about the large Mustang market, they didn't seem terribly interested in competing with all of the others out there making reproductions. Nevertheless, if one wants somewhat unique fasteners, they may very well have it in stock. Their warehouse was huge! I was like a kid in a candy store!