not sure about wheel well replacement panels but when I had my 2000 F-350 I had a minor wreck within the first month of ownership, I was towing a trailer over the Continental Divide and it went from clear pavement to ice on the top of a hill. I was doing about 65MPH and started sliding sideways. while attempting to correct the slide, the trailer I was towing slid around and smacked my bed exact center in the wheel well. Left a nice big crease in the quarter panel. I figured they would just straighten it but the Ford dealership informed me that it was cheaper to replace an entire bedside quarter panel than it was to straighten it or cut and graft a piece in. The damage wasn't the bad at all so I was surprised they replaced it. If you thing about it though all they have to do is cut the spot welds and weld it back on and your done. A lot less time on bodywork.
Check out an entire replacement panel.