There's always three that spawn in the court yard by the church, and three by the courtyard area where the public event happens. When In doubt start a mission and you'll find some underground and in blocked off areas too
Sojourner's Camp, 3 spawn in that area, go there... find the 3 (always on the outskirts of the small area), hop onto your sparrow, travel back to previous area, turn around the moment you see the next area load, return and 3 more will be there
There's a glitch where if you store it in your vault, exit out, then retrieve it then it will count as collected. (might only work for the blue dusk light. Haven't tried it for the green ones)