Virtually all the usual suppliers have them. Here are three from catalogs I have on hand.
LMC Truck for $419 each
Classic Industries $319 each
NPD $445 each
Otto, He has an LCF - Low Cab Forward 5700 'Big Bolt" 2-Ton truck. The LCF fenders are nothing like the pick up fenders and are not being reproduced by any known vendors.