Supposedly a
ZX-6R stator can be made to fit (requires machining of the side cover) . It has a peak output of 25A, but fewer than stock less than 1600 RPM. The
aftermarket Ninja 250 stator from the same people has more power at low RPM than stock (14A vs 11A @ 1600 RPM).
I've never bought from these people and am not specifically recommending them. There are other stator manufacturers as well.