I just flipped through Scotts catalogue and they don't list any patch panels just the whole fender-$595!!! Ya never know though they sell used parts and might have something around.
Did you try this one:

http://www.chevsofthe40s.com/catpagesCHEVS/truckclicksheetmetal.lasso?Dept=Truck

Couldn't find them there either.

I could only see one picture of your truck, do ya have more?? The cab looked great in that one.

Sean