just go to Azteca in cloudburst forest, and Alto Alto. The agave leaves are everywhere there. The leaves will give you nectar. You will just have to keep farming the leaves until you get them. After you farm all that you see change realms and go back through again for more.
When I was doing my Azteca Crafting Quest, I found that just wandering around for Agave Leaves and hoping for Nectar was really boring and frustrating. I had better luck just waiting in the bazaar and getting nectar whenever I could grab it.