Im on xbox 360 live playing halo 3,?

[Victoria?]

and im in matchmaking and i want to play certain games but it says i dont have the map.
how do i get them?

 

[Muzimasta]

Go to the Marketplace and download the maps.

There are 3 Map Packs (Heroic, Legendary, and Mythic)
Heroic is free, Legendary costs 800 MS Points, and Mythic isn't available for purchase yet.

(You'll most likely have to purchase the Legendary one)