In Module 18 these seals are more abundant than previous modules, they can be earned from Queue System's Random: Trail Queue follow-up runs 50, Random: Epic Dungeon Queue follow-up runs 90, Random: Skirmish Queue 60 while a follow-up run 20, and finally Random: Dungeon Queue 45 while a follow-up run 15.
Along with Lair of the Mad Mage and Tower of the Mad Mage granting 40 per boss(Does not include Halaster), and 70 per chest.
Master Expeditions minor bosses can drop 10, while the major ones drops 15, along with handing in the quest granting 30.
Warden Expeditions any bosses from Undermountain Expeditions will drop the same seals while unique bosses to Warden Expeditions will drop 20.
Fragment Expeditions any bosses from Undermountain Expeditions will drop the same seals while unique bosses to Warden Expeditions will drop 20, and the final bosses drop 50.
Undermountain Expeditions all have a chance spawn of a boss where the mobs groups spawn, these ones will give 25.
The Rare Monster Oddments found throughout Vallenhas can drop either 15 or 20 depending on the monster.
Rage of Bel Insurgences grant 1–11(Could be more if fully solo'd) per boss kill, also if you are weekly capped on you will gain 10 from the Heroic Encounter reward.