Crystal Tuning Fork

[item=203426] Can be purchased from [npc=202445] Near the docks of Morqut Village (new hub in 10.0.7). This will cost you 10x [item=190456] and at least level 50 in Dragonflight Jewelcrafting.
Unfortunately, the rare quality item required [item=203404] drops from any mob on the Forgotten Reach, and it is NOT limited to only jewelcrafters. You can get the cooking item, the tailoring item, etc. and each of them are rare drops. Once you find the fork, you can craft the tuning fork, and summon [npc=200743] which is a rare summonable that will drop the pattern : [item=204219]. This pattern in turn, will allow you to upgrade the primordial stone gems for your [item=203460] using 10 [item=204215] and 25 Silken Gemdust (of any rank). This is how you will be able to obtain the maximum item level on your primordial gems.

At the time of writing, 3 hours of grinding elite and non-elite mobs on the island and I have acquired:
[item=203406] x2
[item=203400] x1

several items for rep turnin that are associated with rare drops as well (like [item=202854]). Take note, each of the rep turnin items started off as a treasure map to locate an item and the profession ones did not.

4.5 hours, and I found one. The location of the resonating crystal is on Morqut Islet, just above the quest hub.
https://imgur.com/a/I4ktfBF
Rare has 800k health (rather than the 7 mil that others have). killing him gave 2x 3* ysemeralds, 2x prisomatic ore, 1x 3* neltharite
vault key, few green gems, vault key, primalist BoA token, elemental overflow, and the design unstable elementium

Entry to cave for Amephyst is at /way 31.38 60.71