In 2.4, Commanders were reporting an absence of rank missions when it was the way they were doing the missions that was all wrong, specifically they were tempted to spread themselves over a wide range of systems hoping for the rank mission to pop up. The right way to look for them was to run missions in a tight group, so that local rep was building and a local faction eventually offered the mission.
I am guessing the same still applies - don't wander all over space looking for the mission, keep it tight among a few systems.