I try to look at those as if I were the guy doing the original installation, how I would have done it.
Some guys feed all the lights and drop to a plug and pick up the plugs in the room. Plugs on back-to-back walls are probably fed together. Did you remove the light?
Are the wires in all the boxes the same type? Maybe you have a hidden splice.
Has any work been done on the house? For example, I had a roofer cut a wire and do a poor job of the splice. Is there a long section of wall where a plug might have been covered over. Did you check for power on both sides of each plug that worked?
Did you check the breakers to see if one is dead?
Do you have continuity between ground and neutral? That might give you an indication of which way the panel is in the circuit.
You could short hot and neutral at a dead plug and trace continuity back toward the panel. That might narrow your search. If you get back to continuity in one direction and an untraceable wire in another, you will know what to disconnect when you re-feed.
How about a junction box in the attic?
Good Luck!
