If not difficult, then where / how are they mined? At the hunter's guild? On the game of figs you will find at least some hints, and the poke method does not work right away.
You go to the city of Kielce. To the right is the exit from the city. Select the top line [The Shelter of Resistance]. At this location, bags of Vis are stuffed 1-10k, 1-100k. At the very bottom of Bristia, the Scar. It was at this location that the Feso farmed the most. It is necessary to kill a certain number of mobs (was 7.5k). An announcement appears that the location boss has respawned a huge butterfly Breeze. As soon as she appeared from all the mobs, moonstones of the feso (Moon Stone) begin to fall. When the Breeze's health is reduced by about half, Small Breeze's small butterflies will spawn. They drop Growth Stone (stones 100k. Feso).
If you kill the Breeze boss, the butterflies disappear and the mobs stop giving feso.
They kill mobs until there is not a single mob left, they kill small butterflies and only then they kill the boss.
All mobs in the location are undead (Undead). Mini bosses Small Breeze and boss Breezze - wildlife (Wildlife).
In the Bounty, if you complete all the missions (Normal, Hard), you get a little more than 1m feso = 10 Growth Stone. Always download your second account. For the passage of 2 accounts, you will already have 20 Growth Stone per day.
During the passage of the Bounty, you may have a warp with a bonus room. In it, you need to have time to kill all the mobs and collect the Moon Stones from them all. Sphinx, Minotaur and Medusa before opening such a warp, a stronger Sphinx, Minotaur or Medusa respawns. After killing these hard versions of the bosses, kill all the mobs from which the feso moonstones will also fall.
I came across when two bonus rooms opened in one playthrough.