So, to get to Lampylumen Myriad, you will need to teleport to the Resonance Beacon in Tiger's Maw Mine and head down into the large circular hole in the middle. Once there, head into the cave ...

After Shadows of the Past is complete, a vendor named Shilang opens up the Tiger's Maw Ore shop, and the Weapon Selector is an available item for purchase with Lampylumen ores which can be farmed ...