if it turns out that you cannot get Thunderbird epoxy, I would encourage you to go to your paint place and ask them for clear polyamide epoxy. I'm sure it is sold under many different names, but it is all the same. is a two component system (resin and catalyst). it is used on concrete, structural steel, wood, and pretty much anything else. you will not find a more durable coating that is flexible enough to bend with a bow. you can spray, brush or roll it. make sure you also get the appropriate solvent(usually sold as "epoxy thinner") for reduction and clean up. here is a link to the exact product I've been using for 15 years on bows.
http://www.corotechcoatings.com/product-detail/corotech/polyamide-epoxy