You're going to have to buy an entire door panel. Your best bet would be a junk yard.
Try
www.car-parts.com I would try finding a door and then calling a junkyard and see if they'll sell you an interior panel.
Most of the time, the interior trim panels are junk because windows are left down, other parts are thrown in the truck, etc, etc....
However, even if you could find a crappy door panel, you could unplastic weld the door pocket and reuse it.
HTH's,
Mark