Is there a set about you have to gather from a plot to get a chance for a material drop
I am not aware of any set probability of item drop, but if you keep on top of your guild and admin quests, some reward forging materials. It also doesn't hurt to gather for the sake of resources anyways! Make sure you're checking your inventory, as the furthermost right tab has chests you can open, many of which will have standard materials, state jewels , and hero items. In game purchases and other activities will give you chests for event set equipment material. If you've slain your good share of monsters, make sure to check under "Event Equipment" to see which set pieces you have enough for! I find these methods far more consistent than the very rare material drop during gathering.