labrador tea itself removes 1 COR, otherwise the pet slime you can find just south of the tavern often by exploring will absorb 10 COR every time it mates with you (but don't let it absorb 100 COR...). Oh, there is a star shard in Rasmus's dungeon too, in that tiny room just above the room with that giant sentry robot you snuck past, but yeah, i suggest making more tea.
Also, that holy pool removes 100 COR per playthrough, you exhausted its powers.