I just really want a Ninjask so I was wondering if you can find one in Pokemon white or black 2.
No, you need to trade/migrate for it.
Edit: You seem to be asking a lot of these, so here's a way you can search this up: http://pokemondb.net/pokedex
That link has all the Pokemon in the game. Just click on the picture of the Pokemon you want and it will bring you to that Pokemon's page. Scroll down to the bottom and there will be location data for that Pokemon.
Nope. You must PokeTransfer.
i got my nincada by Pokemon dreamworld so you can get it there too