eebbaayy or a motorcycle salvage yard would be about the only places to check.
Kawasaki.com may have the parts diagrams for your bike.
Partzilla is the site I use & it has a cross-reference.
OEM -->> Kawasaki -->> motorcycle parts -->> year -->> model.
click the part name or part number for the x-ref.
Then search eebbaayy for the various models that use the same part.
1980 KE100-A9. turn signals. rear. diagram ref #19. 23040-033
1981 KZ650-CSR. Competition, Sports & Road.