tried to scan them myself today, since those are the last two songs i haven't unlocked
it seems like the location is random, and it doesn't spawn 100% of the time. used golden instinct with high range to scan the map for tones, even subsumed it on umbra for the last two missions. replayed the quest twice, found only two while spamming instinct all the time (also found 3 ayatan sculptures, didn't know they can spawn in quests), one tone in the first mission and other in the last.
a while ago i replayed the quest and tried to find the tones using a guide with all "fixed" locations and managed to find only one, also in the first mission, though in a different place than the one i found today. i might try replaying it again but with aborting the mission until golden instinct points to an unscanned tone to see if it will work. i wish the cutscenes were skippable on the quest replays.
UPD: managed to find the remaining tones on 3rd replay, one spawned on the ceres mission, other spawned on corpus ship after about 4 quit-outs, both weren't there during my previous quest replays. so yes, you may have to abort the mission a few times before it spawns. golden instinct with >200% range is strongly recommended.