How to get the katana and security helmet?

i have alot of achievements on Halo 3, i have over 1000 Gamerscore from it, and they are mostly from before any of the maps game out, i have all of the ones before any maps came out except for destroying vehicle with 3 enemies in by using equipment and i have none of the achievements from the meta game theing when you have to get 15,000 points in the campaign... any help??