They are out there.. but far and few between.
When they come up on eBay they can get a little pricy.. i've seen a set of rear fenders that needed blasted, few small tears fixed, primed, and painted go for $500+ on eBay, plus shipping.
I haven't seen any new steel body parts available for the pre '47 trucks.. so the secondary market (eBay, swap meets, junkyards, Stovebolt Swap Meet section) will be where you'll have to look.
On an unrelated note.. theres a key to the left of your keyboard that says "Caps Lock".. hit that button real quick for us, would ya?
