Hey there,
Check out subway music or guitars in berkeley, ca. or there web site http://www.fatdawg.com they have a warehouse literally of guitars and parts guitarsI have found some rare parts here its a bit of pullig teeth but if you ask politely they may take a look for you or escort you thru the warehouse. definetly worth a try.
toomanyguitars

If you want an original bridge your best bet is to start watching eBay. Since the bridges of these guitars were held in place by the tension on the guitar strings only, there are a lot of people missing the bridge on their vintage Supro. If you find an original, be prepared to part with $100 to obtain it. High demand and low supply.

good luck, I searched 2 years to find a replacement bridge for my Airline.