Most of the ones I've gotten have been fighting the Dragon Turtle spawn, but that's more of a factor of mass numbers of kills compared to nearly everywhere else on the facet. When I was trying to figure out which Eodon creatures dropped treasure maps for the Treasure Hunter forum, most of the data initially came from the spawn, because the maps were so rare from the natural spawn (and their respawn rate so low) that there was no way to track which creatures were dropping maps unless you got really lucky and got one.