New to end-game

[HEC]

You can buy if from Market Boards (or make it yourself but then you'd need to level up relevant craft classes) and then buy the materias and carbonized matter and shout for crafter to have it Melded. If it's not available on Market Boards shout for the crafter in a city or in Revenant's Toll - you should get hold of someone fairly quickly. You need to get hold of Blacksmith and - preferably - have the items needed for the craft - see recipe here - most of the items are easy obtainable in the game or from Market Boards, the most "rare" one is the Blunt Aeolian Scimitar which is as a reward from leve quest but should be purchaseble on Market boards as well. Then just agree the tip / fee with crafter for the item crafting (you don't need HQ version for the Relic Quest) and as also for the melding of the materias. You can buy those on MB too (or spirit bond your own but that might take a while as it's - partially - luck based upon converting the spiritbonded items). Be sure to get the EXACT type and level / tier of materia needed otherwise it will be not accepted by the Quest NPC!