This is a CQC achievement, under Arena from the main menu. Normal deathmatch rules. If you have less than 8 players, you'll be paired with randoms, and this game mode isn't dead. The best way, if you're able, is to boost this on the way to your 250 CQC wins and your level 50 achievements.
This is obviously not the way to boost wins, but it will help you toward your level 50 achievement.
Searching will be tricky with the randoms. This is much better to do in a group while going for the other achievements. If you get lucky and find a lobby, stay with it (as long as you can stand) because you'll be in the same lobby with the same players after every match.
This will take a while... best of luck!