I will tell you the easiest one, then you post that it is too ugly. :-)
viewtopic.php?f=103&t=25924&p=224499&hilit=1987#p224499
Look at the KX on the left. See if Dennis Kirk or other places still sell the UFO brand numberplate.
Here's one on eBay:
https://www.ebay.com/itm/314538142665
There are old posts on here about fitment on the 1995+ KDX clamps.
This Kawasaki 58029-5018-6W PLATE-NUMBER,L.FREEN fits the following models and components:
Kawasaki Motorcycle 1988 KX125 - KX125-F1 Accessory
Kawasaki Motorcycle 1989 KX250 - KX250-G1 Accessory
Kawasaki Motorcycle 1989 KX125 - KX125-G1 Accessory
Kawasaki Motorcycle 1988 KX500 - KX500-D1 Accessory
Kawasaki Motorcycle 1989 KX500 - KX500-E1 Accessory
Kawasaki Motorcycle 1986 KX125 - KX125-E1 NUMBER PLATE
Kawasaki Motorcycle 1987 KX500 - KX500-C1 NUMBER PLATE
Kawasaki Motorcycle 1986 KX250 - KX250-D2 NUMBER PLATE
Kawasaki Motorcycle 1987 KX125 - KX125-E2 NUMBER PLATE
Kawasaki Motorcycle 1986 KX500 - KX500-B2 NUMBER PLATE
Kawasaki Motorcycle 1987 KX250 - KX250-E1 NUMBER PLATE