Find a fourth. Grind with a full team. Get another member for your competitive scrims.
Iron Sights is a free app that connects you to Call of Duty players online right now. Go online with what you are looking for and what game modes youre trying to play. Or just look to see whos online and message them instantly.
Iron Sights was created with the goal of preventing ranked matches a man-down or playing hardpoint with that guy who only snipes and refuses to get on the hill. Although you might find a longterm teammate or friends, Iron Sights allows you to pick up another person that wont leave mid-game and is hopefully not a mouthbreather.