I'm with you on that one, frustrating as hell. All is not yet lost as they might patch it soon so it works more like MW2?blops. As markface suggested you will have to add friends who play MW3, which wont be too difficult seeing as its one of the most popular MP games on xbl. I often play kill confirmed/domination/demolition etc purely because I am able to join a friends game.

Whats your XBL username so we can add you?