Make them drop from NF mobs commonly. Don't let them drop in non-NF areas. All level mobs can drop them, all drop at a rate of a drop every kill or two (scale it off mob relative level if you want to prevent farming greens).
1) This stops AFK farming that has become a problem in a lot of areas.
2) Provides more reason to roam around.
3) Making it all levels gives plenty of places to hide.
4) Can also leave the Dragon zone drops how they are so you can have another avenue to farm.
5) Take them out of dungeons and other high-traffic quest areas.
