Best approximation I can find is something called Cowl Board. Not quite as thick or deeply embossed but pretty close. Upholstery supply houses carry it in black, LeBaron Bonney carries it in colors other than black, I believe Ford colors. LeBaron says it can be painted so I'm going to try that before going with their gray for the toe kicks & package tray. Local upholsterer is having it come in on their monthly delivery truck.
Bottom row in photo is door panel material.