This achievement can be easily earned by going to the location "Warehouse". Here, you can encounter a ton of missiles to kill, and especially many at the boss battle. During the boss, you can shoot the turrets and they will respawn in seconds. Hence the name of "achievement farming 101"! Update: Thanks to iMaginaryy, you must complete the level in order to completely unlock the achievement. According to his experience, he unlocked it after completing the level. Otherwise, Happy hunting!
NOTE: Some comments below have said that they unlocked the achievement in other levels. Some also have told me that the achievement unlock is slightly delayed. As of this day, it is currently obtainable!