Look on eBay, can find anything there. Also I lived in Germany during the 80s, when you purchase your car, and get it registered with the German state you are in, it’s up to you to go to a auto store and purchase the “D”, it can be a stick-on decal, or a magnetic metal one, and also the screw-on type. Also several different sizes. I even think, as I recall, they were not mandatory. I think it was a pride thing. I know the Netherlands was NH, Germany D, England GB, France F, Spain E, Poland POL, etc. I would look for the magnetic one, case you don’t want holes in your rear boot lid.