Nikon d90 is now a discontinued model?

The fact that Nikon d90 is a discontinued model, does that mean that I should buy accesories right now, like spare batteries, battery grip and etc? Or if I wait, where can I buy them in the future?

If you buy the grip, the battery problem goes away - you can use AA's as well.

It is not discontinued:
http://imaging.nikon.com/.../dslr/d90/

Accessories like batteries or battery grips will be available for a long time, don't worry about it. Even if it were discontinued, Nikon would keep supplying these things.