Make your own
You say (I think) that you have the frame already. What makes you think it is a standard setup. It may or may not be. Your best bet is to have someone make one for you or build one yourself. The cost of building one yourself is about 1/2 and you get all the extras where YOU want them. There are lots of books on the subject and all you really need is a standard sewing machine (I use the admarals). I found that once I get the design part done it only takes a few hours to sew one up. Since this would be your first "project" I'd recommend not skipping the pre-fitting step once you have all the major pieces sewn together. This is the same as tailoring a dress/suit. This really makes your final product "look professional".Once you "get the bug" you will be thinking about sheet bags, weather cloths, winch covers,... the list is endless.