I see post #11 has your answer.
When you buy parts for the Crossfire you should see if the part number is on the part you require. The license plate lens has this Mercedes part number on it, 230 820 01 66.
When you do a Google search using just this number you will come up with a lot of sites, some of interest and some not so much. This can give the prices of various sellers and availability. The site I give has a cost of just less than $10 each. CLICK