Goodmarks should have pretty much any panels you need, keep in mind they are repros and wont quite have the quality of fit as a factory part, and may take some modifications to fit properly. Overall probably the nicest parts your going to find.
Oh yeah, BTW i have plenty of parts sitting around for 67-72 c-10's and burbans, so if you cant find what you want, hit up my email, i just may have what your looking for.