I suggest creating bar events where some npc may give the player a hint where to look for those lvl7 officers, for example for 5 story points and 1 million credits this npc can send you to a constellation with lvl7. Because I for example even after 90% of the sector explored can find 1 of them max.
Something like - Long ago in X constellation was a big battle where Y fought Z and both of them lost a lot of skilled pilots.
Or like this - My old friend, an extremely capable fellow has gone missing in constellation X, people say he's long dead, but I know he's there somewhere.
You get the Idea.