If you can get the small parts, great, or try eBay and junkyards.  A junkyard probably won't part with just pieces of the frame unless the rest of it is banged up.  Bestop's Supertop comes with a new frame but then it costs more than the Replace-a-top and the skin only works with the Supertop frame, so you have to keep that in mind when it's replacement time.  There are also a couple of tops out there that use the rollbar as a frame.  I don't care for the looks of it myself but that's a matter of personal preference.