The (old) Onion Set?

[Felis]

There was also a black helm with red feathers that was obtainable via a quest NPC in Gridania, back in 1.0-

Peregrine Helm

It was not really a quest
Enemies started to drop deaspected crystals and nobody knew what to do with them. Even NPCs talked about it. Some update later a NPC showed up in Gridania who gave you the helm for a specific amount of the deaspected crystals.
A suspicious Lalafell. He said he want them for science. I think he ate them.

[Wobble]

Which level of exploration have people gotten them from on retainers?

[Baneus]

Which level of exploration have people gotten them from on retainers?

Quick. They normally bring back random fish and house parts, but occasionally you get cool stuff. Examples of stuff I have had:
Mog weapons (I just about have all of these now)
Primal weapons
Darklight gear
Warwolf gear
Red Onion helm (not sure about the rest of the set)
Dungeon drops (I've had manor vanish multiple times now)
The house items have a chance to be two and three star.

[mbncd]

The good thing about quick ventures is gear and retainer level don't matter at all (so long as you've unlocked quick ventures, which is a level 5 or 10 thing I think?) so everyone has a chance to get them, even newbies or people who were late getting their ventures started.