Best place for Mod unlocks some will say is Canthan Chest runs, most popular being in the Nahpui Quarter area. Decent Purp to Gold ratio, and though the weapons can be nonmax and have stupid stats, the mods are decent there if you open enough.
Hopefully this helps, I've wandered a bit back and forth off topic but meh ^.^
I dont know about farming places, but I've unlocked half of my runes and mods from drops/chests through general play. The rest have been gained through Balthazaar Faction from pvp.
If money is no option, then you can always buy unidentified runes from other players and id them yourself ^.^ It'd be quicker I'm sure, but then it will likely cost a lot. That said, farming chests will cost a lot too...
Critter-wise I'd guess Ettins+Giants(+Trolls?) are best for rune drops, however I'm not certain of that.