On JP, Lumincrystal Grania was added to the Prize Medal Shop (where you spend Armada medals) shortly after the release of The Primordial Darkness UQ. It costs 500 gold medals each and has a limit of 1 purchase per week.
This might be something that was overlooked/forgotten about. I would like to see this added to the shop as it would help with building our 6 Klauz weapons that we're going to be getting. (2 more are coming from the Sodom solo fight)
Swiki page (JP): https://pso2.swiki.jp/index.php?交換ショップ%2Fメダル交換ショップ