Samurai Clan Mask is a mask that unlocks when you upgrade Samurai Clan Armor to level III. You do not hunt for it: improving the armor adds the mask to your gear.
Own Samurai Clan Armor, upgrade it to level III. The mask appears in the Mask slot right after.
It matches the look of Samurai Clan Armor, but you can wear it with any outfit.
Adachi Dragon Mask
Adachi Dragon Mask is a New Game+ mask sold by Baku the Voiceless for 5 Ghost flowers. It does not exist in a first playthrough.
Adachi Half Mask
Adachi Half Mask is a mask you get by finishing "The Sister Betrayed", from Masako's tales, part 9 of 9. It is a story reward, so playing the tale is the only way to add it.
Ancient Dragon
Ancient Dragon is a New Game+ mask sold by Baku the Voiceless for 5 Ghost flowers. It does not exist in a first playthrough.
Avenging Lord
Avenging Lord is a mask waiting at a Gift Altar once you finish "The Broken Blacksmith" in Jin's Journey. Each main story milestone unlocks a different altar mask.