How do you unlock all zombie maps on xbox 360?

You have to purchase them on the xbox live marketplace. Some of them like der riese and I think like 3 others you have to of bought the special edition of Call of Duty Black Ops (i'm guessing that your talking about black ops Zombies) and with the special edition you get a download code for the other maps. For some reason treyarch has decided not to release those maps on the market place.