I've seen them on eBay quite freguently, but they are not cheap. Try a search for "Fulton Visor" There are also aftermarket versions available, but again, too pricey for my tastes.
As shadetree as it may sound, I'm going to try to make my own from an extra hood I had lying around. If I ever get around to it, and it turns out looking half decent I'll post some pictures.
