If you can get a good clear picture of the tank with the graphics on, you could just go to a signage place and they will make you a copy. I do that with all my graphics and it means that if they get damaged I can just ask them to make some more. My sign place made the noguchi decals for me and various other decals and I have been very happy with them. The only problem with the decals they make for the plastic tank model bikes is that they dont last long as you probably already know about stickers and plastic tanks.
