If your lucky you can find the name of the company on the ends of the door someplace. Each company makes there's differant.
My guess is your looking for what was once white grids on the outside of a steel door.
Most likly it's a Stanley Door, any lumber yard can order you one. It's not something there likly to have on the shelve. Before buying it take a good look at the door. Lots of times the paints failing and rust has set in so it would be better to just replace the whole door.