The only early mage gear I've been able to snag is from Nirya (annoying Altmer) in the Mages Colleges. Join the DB and get your double sneak attack gloves. Since she's not essential; slip on your muffled shoes and your backstab gloves and power attack her into oblivion. Pluck those expert robes off of her at level one. Pay Tolfdir your 250g and your back in the guild with some snazzy expert robes of destruction; you wouldn't normally have access to this early. I know you can deep six Brelyna Maryon and get her hood and staff, but those aren't necessarily worth it, but they are free upgrades for minimal work. More importantly though her free magic resistance jewelry is worth it; so do her quests before you off her.
Sergius Turrianus looks like he's wearing Adept robes so I doubt he's worth the trouble, but I never bothered to kill him and check. I'm pretty sure excluding the other two students J'zargo and Onmund; everyone else is essential or is a vendor/trainer.
In terms of non-college wizards, with the exception of Nelcar (who's essential) every other mage I've encountered wears the basic blue robe.
Anyone else know of some choice pieces you can get early on? A master robe & adept hood out of the gate would be nice, but seemingly impossible to do legitimately.