If the kit was from Denny or Skystar, they didn't provide bills of sale with the kit. There is a letter and form on the FAA website that you can send in with your other info, and the FAA will accept that in lieu of an original bill of sale. I did it last year on my new Kitfox 4 build and there was no problem with it from the FAA. The kits were sold in various arrangements. You could get quick build wings, firewall aft, firewall forward as well for that matter. Don't think they ever sold individual sections of kits, like wings, fuselage, ect. Here is a link to it. Look at the second one from the left. Obviously, completeness of the kit is important. But depending on price, most anything can be found on the used market or built. Kitfox does sell quite a few parts for the Kitfox 4 yet as well. JImChuk
Downloads – Kitfox (kitfoxaircraft.com)