You can get both Kyurem forms on Black 2.But trading is involved.
First, you need to catch Kyurem, at the Giant Chasm after defeating Team Plasma and the Elite 4 round 1. You also must have the Wedge Of Gene. Ghetsis should of left this behind after you defeat him. This is the key to getting Black Kyurem. Then, go to Victory Road. Search around until you see Zoroark. If you don't know what it looks like:
Then, follow the Zoroark, until you come across a castle underground. If you played Black and White, you should know this castle belongs to Lord N, The King Of Team Plasma. After he disbanded Team Plasma when Ghetsis lost his mind. Follow N to the main room, then you will battle his Level 70 Zekrom. Beat N, and he will give you Zekrom in the form of the Dark Stone. Take it to Dragonspiral Tower in Iccirus City to the top floor, and then you can catch him. Then, get Zekrom and Kyurem in your party, and use the Wedge of Gene on both of them. You should now have Black Kyurem!
To get White Kyurem, you have to trade Reshiram from White 2.