We have a plastics shop in Richmond that can make just about anything. We have had 4 or 5 windscreens made for Active Thunders using a take-off for a pattern. They have been making them from Lexan.
I think that if you make a pattern out of corrugated cardboard, you can probably have any good plastics shop make one. A sign shop may be able to help you as well. If it has bends to it, you will have to heat the bends when installing, and hopefully the plastics shop can assist/guide you in doing so. I would give you the name of the place in Richmond, but they are pretty much "hands-off". They just make it wholesale, and leave it to someone else to install it.