Unlockable CO's in War Room
Once the characters are unlocked you still have to buy them from Hachi, the cost is listed at the end of wach CO's how to unlock.

Sasha - Beat Mission 20 in Normal Campaign 1000 points
Grimm - Beat Mission 20 in Normal Campaign 1000 points
Javier - Beat Mission 20 in Normal Campaign 1000 points
Lash - Beat Mission 26 in Normal Campaign 1000 points
Adder - Beat Mission 26 in Normal Campaign 1000 points
Flak - Beat Mission 26 in Normal Campaign 1000 points
Hawke - Beat Mission 26 in Normal Campaign 1000 points
Zipo - Beat Mission 26 in Normal Campaign 3000 points
Chakka - Beat Mission 26 in Normal Campaign 3500 points
Candle - Beat Mission 26 in Normal Campaign 3500 points
Nell - Beat Normal Campaign with an overall A rank 2000 points
Hachi - Beat Normal Campaign with an overall S rank 2000 points

Hachi's Land
Buy for 1 point when Advance Wars 1 is inserted in your DS

Nell's Land
Buy for 1 point when Advance Wars 1 is inserted in your DS

Advance Warpaper
Buy for 1 point when Advance Wars 1 is inserted in your DS

Strum's Land Map
Buy for 1 point when Advance Wars 2 is inserted in your DS

Lash's Land Map
Buy for 1 point when Advance Wars 2 is inserted in your DS

Advance Warpaper 2
Buy for 1 point when Advance Wars 2 is inserted in your DS

Unlock Mission 11 (black boats)
On mission 10, capture the city east of your HQ to reach mission 11. (The black boat level)

Unlock Mission 14 (black bombs)
On mission 13, capture the city in the northeast corner to reach mission 14. (The black bomb level)