As far as I know, there is no visual list that shows which local unit can be recruited in specific regions for each faction. You have to check the ...\mods\SS6.3\data\export_descr_buildings.txt file for each unit, there you will see entries like:
Code:
recruit_pool "Prussian Axemen" 1 0.17 2 0 requires factions { teutonic_order, } and hidden_resource prussia
recruit_pool "Prussian Axemen" 0 0.085 1 0 requires factions { teutonic_order, } and hidden_resource hre
recruit_pool "Prussian Axemen" 0 0.085 1 0 requires factions { venice, scotland, england, france, portugal, spain, aragon, moors, milan, papal_states, sicily, hre, norway, denmark, poland, russia, lithuania, kwarezm, turks, jerusalem, egypt, byzantium, hungary, kievan_rus, mongols, slave, timurids, } and hidden_resource prussia
That means Prussian Axemen can be recruited by the TO in prussia (higher replenishment rate) and regions that have the hidden resource "hre" (some german settlements). All other factions can recruit them in prussia only (with reduced replenishment rate).