I assume you're referring to a shield (by 'plaque')? If so, your best bet may be to look for an old damaged knife (same vintage and/or model, with a salvagable shield still on it) on the 'bay or other secondary market site, and swap the shield from it into yours.
I doubt Boker would be able to source something that old, but it may be worth contacting them to see if they can steer you to someone who might.
David