from March 19 you can buy it
or download it I'm not sure but probaly buy
Chat with our AI personalities
the zombies
The stimulus package and the Resurgence map pack
All the Map Packs were released last year before the November 2011 release of Modern Warfare 3 and there will not be any new map packs. First Strike, Escalation, Annihilation, and Rezurrection were the names of the Call of Duty Black Ops Map Packs that were $15 each and sold only for the PC PS3 and Xbox 360 . Activision never sells map packs except for the newest game and Modern Warfare 3 is the newest Call of Duty Game and just starting to have map pack available for it.
There is no map packs for the Wii as far as I know.
I have heard from several sources that the map packs will come out on March 29th, or March 30. Or possibly in that time interval.