Panel doors show up on ebay and craigslist once in a while. A nice door was on craigslist last month for under $100 and was in great shape with the tail light. Most of the doors are damaged or rusted. Hard to find a good one that you don't have to repair. I would not let it stop me if that's what I wanted. Doors will show up.

You may want to check with some of the panel truck guys, I think that the doors are the same from 1938/47 but I am not sure about that. It might be from 1939/47.

There's a couple of 46 panels on ebay that you can compare to.