Body panels new or used

Replacement body panels.

I am restoring two Ex Skoda Challenge Favorits.

Both are fundamentally strong but the forests have taken their toll on the floorpans and chassis rails.

Looking like we will be able to get one up and running with minimal body work, looking like a couple of rear arches and some tidying up on the floors..

The second one needs to go back to a bare shell and a lot of TLC...

Where are the best places to source replacement panels and for those not in production has anyone got anything in stock secondhand? 

If someone is breaking a Favorit are the floorpans likely to be rotten or are the road cars quite strong there? 

Kindest regards

Simon