I dunno if you have a thing against all these designs, but mrbodykit.com has m3 and bullett fenders, all fiberglass. I dunno where to get "stock" looking fiberglass fenders.
if you have the # call them...sometimes they have things that aren't on the adss and all....also try mustang parts specialties...i put the # and other info on another thread earlier...about the wiring harness...it IS better to call these guys.