It's not common at all. You're quite right.

We don't attempt to teach the skill to those who have no pre-existing aptitude. Occlumency, yes, for defensive purposes. Legilimency, however, is a waste of training time in people with no predisposition.

Bellatrix seems certain that this Procyon is a natural talent. That does not, of course, mean he is untrained nor that he has gone undetected all his life.

Bellatrix may have thoughts on ways to trace him.