Motosport.com is excellent. I use them for my dirt bike too. They are one of the site sponsors as well.
Speaking of, be sure to check out the other site sponsors listed on the forum start page.
Cycle Gear has some stuff for the Ninja 250 as well.
And finally, ask around your local Kawasaki dealer and see what they have to offer. (And if you don;t plan on doing your own maintenance on your bike, now would be a good time to make friends with their service manager/dept.)
I have come to terms with the possibility of dying while riding, life has a 100% death rate. I would rather live having fun and end up dead in a motorcycle crash than never do anything fun because it's dangerous and I might get killed. No one makes it out alive anyway. - From a friend on another forum, used with his permission.