There is one way to get gear from overland content, apart from quests, and that is the treasure chests that very infrequently appear in leves.

Also, Grand Company Seals can be exchanged for gear while you're leveling, in a similar way to the Tomes mentioned by Muse, though truth be told you're unlikely to get sufficient Seals to get gear which is still going to be useful at the level you manage to get them.