Hi!
Any single-player mission will work with this script as a coop
http://forum.1cpublishing.eu/showthread.php?t=34939
Also someone posted a coop mission pack several months ago to be used with a previous version of the script. Maybe in MP section.
It is also easy to create your own missions in FMB if you start with opening and editing existing missions - just change aircraft types or waypoint locations.
If you do not want to use a script just place a spawn-area (spawn place) object into the mission you want to fly in MP.