I bought my lexan by the sheet from a company in San Diego, and all thk's were available clear, grey, black, and white, IIRC.
http://www.eplastics.com/Plastic/Lexan_Polycarbonate_Sheet.
They will also cut the pieces per blueprint if you wish. I used a skilsaw.
Problem is forming it. It's easy to do if you have a big oven. Most folk don't.
You clamp it to your existing glass, then put in the oven at ~250F for 4 hrs to get the water out of it. Then you bring the temp up to 300°F? to actually change the shape. If you don't do the water thing, it can end up with bubbles in it. I did my Windjammer fairing many years ago, and learned the bubble thing the hard way.