An easy way to get this is to set up a custom match with a friend.
Set a custom match 5 mins max or 100 points (10 kills).
Start on first map (1 of 6) and take it in turn to win on each map and then move onto the next.
This will also help towards over kills as well and number of online games. It will take about an hour or slightly less if one person can knock out 10 kills quickly.