There are a total of 6 BLAST Soda Cans available on Halo 2 Anniversary MP maps. It is recommended that you use a Sniper Rifle to destroy them, and they are easily done in Custom Games.
On Lockdown, it can be seen by following the large crack in the ice in the middle of the map if you are looking from the top of blue lift. The ice will need to be shot down first. It can also be seen in the video below.
] - Lockdown