[Fate]

When you take any province except a capital it has a local poptype that gives it recruitables (barbarians, generic commanders/light infantry/etc...). Some provinces allow you to recruit Mage commanders (They will be on the side of the commander list, greyed out).
To actually recruit them you must first build a lab (by moving one of your mages from your capital to that province and selecting build building -> lab, should cost 400-500 gold).

Non-indy mages are mages you get from your forts. To build those you need a fort and a lab (and a temple if they are sacred/have holy paths). Some mages (and units) are capital-only, provided by your starting sites (They show up next to your starting buildings in your home province). All the rest should show up along side any local populations in any fort you build (except for land nations building forts underwater/water nations build forts on land).