There are alot of people in the 30 and not all can be on your friends list. To find these others, when you go to your MW3 friend list by hitting "Y", you can then arrow to the right 3 times. It then shows your most recent lobby players, then Facebook friends (if you are linked with that) and finally clan mates. Go here and send voice messages to a few asking to party up and make sure you are mentioning you are a member in the 30. 9 times out of 10 you will either find people to match with or they will grab you after their current game, or worst case add you going over 6 party members and play ground war until someone has to go.
30 members are really good about trying to get everyone into games and together.