I got a MOAB in a game of Domination on Village. I ended up getting it using a gun I thought I wouldn't use in MW3, the UMP w/ silencer running the specialist package. The only downside is, it took me until a score of 194 to get it but, a MOAB is a MOAB regardless of how long it takes to get it.
If you're interested in watching a fellow 13th member's MOAB, you can check my vault on PS3
PSN: Them__Bones (two underscore)