'31 Model A 4 Door

[Spiffy]

I just purchased an early '31 4 door Briggs (now learned it's a Murray) body. (not a slant windshield) The subrails are missing and the piece of the body that goes under the doors from the cowl to the post with the door latches and back to the rear door jam (like a rocker panel type thingy) is missing. Does any Model A parts supplier make that part? I've done searches for the part but can't find it. Sorry for my lack of Model A knowledge, this is my first one after lots of fat fendered Fords. The part I need is shown in the picture below--under the doors. This isn't my car, just a picture I found.