Two options I know of:
- harvest in the zone that has the required level of mat you need. Even if you have maxed out crafting, you will still see 50/50 split between the mats at your crafting level and mats in zone level.
- reset your crafting skill on an alt to farm the level of mats you need.
Is there a way to level lock a character so I don't out level the crafting nodes I need?