Due to the changes in world mob drop rate, stigmas like Enmity Swap are nearly impossible to get now.
There's no instanced dungeon that can realistically drop it (stigma is too high level for Haramel and too low level for FT), and you will likely level beyond lvl22 world mobs that would drop it well before you see any stigma drop, let alone the one you need, especially with double XP.
You could almost certainly level eight toons from 20-30 with the specific goal of getting this stigma drop and never see it at the moment.
Personally, I would consider all low level stigmas impossible to get - your only chance is to buy it off a player who received it pre-nerf. It's actually a running joke now, level 28 "common" stigmas like Word of Protection are selling for 30mill+, more expensive than best-in-slot endgame gear, because they're literally harder to get than the best gear in the game now