well u can get some for motorcycles which are similiar made from fibreglass and metal but they are way to large , they would have to be modified a lot because of the tire sizing. so i think u would be better to start with a fender that fits the bike and add to it using metal. u could use around 18 gauge cold rolled steel . i would do the sides first by laying the fender on a piece of construction paper tracing the fender twice to make a complete circle , that will be your sides with lots extra room to cut the shape you with at a later point . then i would begin to slowly fill the front and the rear . the 18 gauge is thin enough that u can bend without having to have english wheel or planishing hammer . u can just bend using a tube or pipe around the same diameter of the fender and bend it over that to get the roundness to match tire. then piece in the rear and front . weld in and fit as u go along , it will take some time but it is doable , hope this helps u some.