This thread will tell you what materia you need to upgrade your gear:

http://forum.square-enix.com/ffxiv/t...ciples-of-Land

As for what gear drops the materia, I have no spreadsheet but ilvl 55 gatherer equipment can drop tier IVs, and the tiers I through III are dropped from other gathering gear of various levels (gear that has Perception, Gathering, or GP on it). As far as I can tell, any piece of gatherer gear can drop any type of gatherer materia; you won't, for example, always get GP materia from rings.

If you want to craft your own accessories, Leatherworker is the best DoH to level, as that craft provides rings, neck, and waist for gatherers (Goldsmith provides wrist and earrings). Leatherworker is also useful for crafting many pieces of gatherer head/body/hand/legs/feet gear.