I've heard of people making their own blades... I think you can even find "PVC Optimized" designs online for making your own. There was a guy that built his own wind turbine and had one blade fail due to 50+mph winds. I don't think it had lasted long enough to have UV problems. Check out
his web site. I would think if you wanted them to hold up you may be able to make them, then sand them and coat with a couple layers of fiberglass with resin. It will protect the PVC from the sun, and add substantial strength to the overall blade.