Marverni has three types of mages: Sequani Stargazer, Gutuater and Druid. Vergobrets are priests, but not mages. Gutuaters and Druids are both mages and priests, which means you need both a lab and a temple before you can recruit them, but their upkeep is half of what it would be for a non-sacred unit (1/15th and 1/30th of recruit cost).
All Marverni mages can be recruited in all their forts (castles), including the new ones they build. Marverni has only one starting site, "Carnutes", which lets you recruit Boar Warriors and Boar Lords. You can't recruit them from your other castles.
Indy mages can be part of the defenders (druids (but these are just nature 1, holy 1 mage-priests, nothing like YOUR druids), Wolf Tribe Shamans, amazons) or just random mages that you can't recruit after you conquer the province (Wind Lord, Bloodhenge Druids, Azure Mage Initiate, Wizard). When you send your mages site-searching, some sites will give you access to new recruitable units in that province. Better independent mages are often only available from magic sites.
And finally, if you haven't done it yet, research Evocation 5. Evocation 4 will give you Blade Wind. Evocation 5 Will give you Gifts from Heaven. They don't take any gems, and as you already have Summon Earthpower (conj 2) researched all your druids can cast either spell...
