Among them are Ruijsink, Lely and Eckert, but there are many others. As you note, they do not typically travel with their students. Then again, Lely was present when his student Pijus Labutis won the 10ball at Derby City this January.
Good instructors are few and far between. Any decent player can instruct a beginner and actually bring them pretty far. Training in advance player is a whole different thing. Those instructors really would be few and far between.
The ability to play also does not make a good instructor. I used to have a world champion player came in my poolroom every day and gave lessons off and on and I'm going to tell you they were terrible. In fact I used to lose customers cuz ultimately he'd end up borrowing money from them and trying to pay it off with lessons.
