We could make CV's spawn at a set intervals from ports.  This could be configurable, ie the first one after 15 mins, the 2nd after an hour, the third after two more hours 4th after 3 more hours, etc.  or it might be as simple as one per hour.   So a single port could spawn more than one cv (max number would be configurable and might be set at 1 for some areanas).  If an enemy took control of a cv, it would not prevent the port from spawning another.  
Thoughts?