If you don't have the original panel to use as a pattern, you can still make your own panels by getting sheets of masonite from the hardware store. First, measure the distance from the bottom of the inside of the door to both shafts and from the front of the door back to each shaft. Be sure to hold the tape measure parallel with the bottom of the door.
Layout the holes based upon those measurements and cutout with a jigsaw.
Now you can hold the piece of masonite up to the inside of the door and trace the door structure on the backside with a pencil.
I suggest undercutting your trace marks by 1/8 of an inch to accommodate the forthcoming upholstery. You can use a circular saw with fine blade and cutout the rounded corners with a jigsaw.
In order to locate the panel fastener clip holes, you need to offset the holes in the masonite by the amount of center to center axis of the fastener clips. I think it is about 1/2 inch.
I taped long paper templates on the backside of the door and punched the holes out, then transferred the paper templates to the masonite. (this duplicates the location of the holes in the door structure, so you need to just mark a centerline at each hole and measure back toward the center of the door about 1/2 inch).
In order to locate the two holes for the door armrest, I got a large screw with the same thread as the armrest screws, cut the head off and ground that end down to a point. Now screw those in and hold your masonite up to the door and smack the masonite with your hand and it will make marks on the back side of the masonite. Drill those out with a 3/8" drill bit.