We purchase our fenders from ICON. They have a large selection and their quality is fantastic.
then click on single fenders. hope they have what you are looking for.
NOTE: When installing plastic parts on your rig. always drill out the screw holes a bit larger than the screw. Plastic expands faster than the metal side and contracts quickly and flexes on an RV. Give it room to move and expand. And just snug the screws do not tighten very tight. Most are installed at the plant by just running the screw right through the plastic fender at the indent marks.