In our ROO, there was a label inside the canvas bunkend with the manufacturer and location. Suggest you check for that first for a contact. If no luck there, contact Keystone and see if that can give you the manufacturer. If all else fails, the next stop is likely a boat canvas/awning company. Agree that they should be able to take your existing awnings and use for patterns.
Re replacing the bunkend decks....DH helped a friend do his and it's not brain surgery by any stretch, but takes some good muscle. They're fairly heavy, but bulky and awkward to handle and get lined up when time comes to start attaching. Round up a couple of friends and you should be good. IF those bunkends actually can be dismantled, you may be able to find the material that's used inside and remake them yourself...maybe save a $ or two. Good luck. You're not the first one to buy a pre-owned camper and find some surprises.