From the diagrams at Partzilla the part number is 23037-1031. I saw one on EB but it's pricy >> has make offer button. So you could make an offer, but don't be influenced by the list price. There's also a used one that appears to be in good condition.
I know you'd prefer oem, but K&S makes reproduction Z1R rear turn signals. #25-2146. not sure about the front. DennisKirk lists them & I saw one nos K&S turn signal on EB. Assuming you can trust the reviews, various buyers were pleased with the K&S part.
Edit: Also, I saw Doremi Collection turn signals listed on Web Bike Japan. #50020. I'm not sure if they're K&S or what. From the site:
DOREMI COLLECTION lineups mostly KAWASAKI Z series model parts and also reproduced genuine parts now unobtainable! Must-see parts for users who want to maintain their vehicle in a perfect condition.
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