I think the "apprentice" angle really shouldn't be understated. Yes, the odds that a random Jedi in hiding finds another person with force sensitivity to train might be astronomical. However, the Force does not care about probability. It knows where you live, and can't compel your action but can whisper loudly and obnoxiously in your ear every time you try and relax. *ahem*
Also potentially relevant angle: Inquisitors and other miscellaneous Dark Side adepts. When the Emperor died, Vader died, and the Empire fell, the structure they were indoctrinated to follow disappeared. Its not impossible that a non-zero number reacted by doing something more constructive than "Get killed" or "Go be an independent villain".
( The more I contemplate the topic, the more I really, really hate the Sequel Trilogy's obvious desire to wipe the slate clean. Its the laziest, least creative method of creating a setting for your story. . . )