Probably the best bet is to check out the local RV dealers. They carry all kinds of canopies for RVs and would have the track to mount it onto any RV. By the way, from your question, I get the feeling you have a canopy and are just trying to find a mounting system. If that is the case then try to find the mfger info on it and contact that company directly or check their website to see where you can find their line of products to go purchase it. Long items like the track may not be suitable for the USPS so if the drop-ship what you order at the RV store, you can pick it up and begin to mount it.
You might be able to take the canopy you have to the RV dealer and they may be able to identify it unless it was a hand-crafted item but still may be able to check to see what size mounting you need for it.