I want to change the lenses in my rear pods
First of all, we hope you're planning on putting amber ones in there. Clear lenses are in violation of the US government's FMVSS 108 vehicle code. Google it; it's smashing reading. You have to go by your local government's regulations, but most states, and Canada, follow these guidelines.
In that same vein, FMVSS 108 calls for nine inches between signals, center-to-center, and you're going to have a difficult time getting that on your 250 Ninja. Of course, neither of those things keeps people from changing their signals around. You'll just have to decide for yourself what you want to do.
There's also a matter of safety. The board standard line has always been to disencourage people from putting their turn signals in those rear pods. The long-term members of the board believe that having your signals spread out wider makes you safer and more visible. You can always move the stock signals up and in, such as in this photo, or buy a type of signal that you find more attractive and use it. They'll have the advantage of being legal, as well. See the streetfighter article for turn signal sellers.
Amber and clear lenses are available from Keith @ Asian Cycle. Keith sells good quality products at fair prices. For rear lenses as well as lenses for the stock turn signals, make a call to Clear Alternatives.