Yea, hidden dungeon in chapter 2 has them. It can be gotten from the shrine maiden/miko enemy in 2-5. Which I felt I got lucky getting since you can only fight it 3 times a day for a chance at the map to even drop unlike chapter 1 where you could go at it 50 times a day to try to get it.
I only unlocked it a couple days ago and despite clearing all of the stages to get the 4th tier units, I still have yet to actually get one. Which really sucks since I'm quite stuck in the game right now and upgrading units would be the biggest jump in strength I can do.