Can this drop for all vet rank levels or is it only v12-14? Also, what is best place to farm for this other than cyrodil chests?

Vet 11 is the lowest I've seen, i didnt know it went that low honestly. But craglorn chest will drop it too.

In the cracked wood cave, the drop rate is high, like Adam said, from vet 11 it starts dropping, but I believe it goes up to vet 12 in this cave.