When I needed a window for an old camper van I went to a boat specialist. They can usually make any kind of window.
I make heaps of boat and one off type screens from Acrylic (plexiglas).
You can just roll or shape a piece of sheet metal about 1.6 mm thick to the shape you want then line it with polyester cloth (like sweet shirt material) heat your sheet to 135 to 140 degrees C and lay it on it. Done - easy aye !
I saw heaps of Hi tops in bali and Thailand a few months ago when I was there but I wouldn't like your chances of exporting one from there, I'd try Suzisport in Aussie as they got some hi tops over there too they might be able to help.