They stopped selling premium a couple of months ago. You can still purchase the DLC for MW3 separately and you can purchase the DLC for BO2 either separately or by getting the Season Pass for BO2. Elite for BO2 will be free.
Just my opinion, but the DLC sucks. I wouldn't waste your money.. I regret purchasing elite because I play with DLC disabled unless I'm in a party and I can't disable it myself . I really didn't like the maps, some might, most don't from what I've heard.