Past week I've been soloing Lair Reives in Foret for Peacekeeper's Coalition and I've gotten 2x Yorcia Visage IV's and one Yorcia Visage V. Maybe in about 12 runs I've gotten those 3 heads.
I have yet to see any Yorcia head drop from Ceizak and Yahse, but plenty (1's and 2's) in places like Marjami, Morimar, and finally Foret. I think that only Cirdas and Rala heads will drop from Ceizak and Yahse, while the other zones will drop the new simulacrum heads.