http://www.ebay.com/itm/Kawasaki-Ninja-250R-08-12-Helmet-Lock-/131304471133
http://www.ebay.com/itm/Kawasaki-Ninja-300-250-13-14-Helmet-Lock-/131304472064
This is pretty similar to what I bought (in fact, this must be a knock off of OEM lock in Taiwan/China). The only thing is that it won't come with Kaw OEM keys. If their keys are the same size (length, thickness, and width), you can still re-key the lock to accept your ZX key, I believe. Otherwise, you need to carry a separate key for the lock.
1973 Suzuki GT250, 1976 Kawasaki KH500A8, 1979 Yamaha RD350, 1985 Yamaha Maxim700X, 1987 Kawasaki EX500, 1994 Honda CBR600F2, 2004 BMW R1100S, 2005 Kawasaki Z750S, 2003 Suzuki SV1000N