I've managed to make a repro shooter cover for mine.
The process was:
1. Scan an existing plastic and touch up in PhotoShop (or use Firebrands images that he's offering up)
2. Mirror the image that you've scanned. We actually adhere the image onto the back of the plastic and then spray it's backside so it has to be mirrored otherwise the completed plastic will be back to front.
3. Print the image onto some clear adhesive backed Vinyl
4. Adhere the vinyl onto a piece of Lexan. I seem to think I used 1.8mm thick. You need to take your time over this part as it's easy to get air bubbles under the vinyl.
5. Cut the Lexan to shape and size. Luckily the shooter cover was just a rectangle. I'm going to have fun when I try to repro the base plate below the Nell Assembly.
6. Use some White Matt Plasticote spray paint to spray the back of the vinyl. I put 3 coats on mine.
That's it. Have to say I was quite pleased with my repro.