Fork gaitors on E bay.

[pekingduck]

Maybe I am wrong, but the top shelf gaiters, like from Kawasaki and Triumph, are a rubber composite (or was it pure industrial rubber?) that outperforms the plastic alternatives. They are not cheap $$$, but worth the investment since they appear to last. I had the Kawasaki offering installed on the 2014 CB1100 and the bike was not sheltered from the sun day in and day out Monday through Friday in the profuse, hot, humid and blazing summer sun for years.

GO, not sure exactly what they're made of, as they're shinier than rubber and more durable, but still very tough and flexible. Likely a combination. The real rubber ones I had on my old Triumphs and BSAs would only last a couple years before they would dry out and split at the folds.