Source of spare wheel panel

I'm repairing rust on my 37 Roadmaster. Been looking for replacement panels for the bottom of the sidemount wells. Does anyone know the source of the replacement panel Precision Restoration shop used in 2011 to repair a 38 Special?
Thanks

 

Looks like a.trailer fender.

 

It sure does

 

Had thought of a motorcycle fender, but you may be right.
I'll search for a fender that meets my dimensions.
Thanks

 

i'm thinking Northern Tool

http://www.northerntool.com/shop/tools/category_trailers-trailer-parts+trailer-fenders

 

If you have a local Tractor Supply Co. near by they stock the trailer fenders.