Wiki says that originally Urania, Rusalka, Boreas, Perun, Indra, and Nergal can be gotten with gems. Then after June 30 (~3 months after launch), Orpheus, Mephistopheles, Astaroth, Undine, Zephyros, and Baphomet were added. No other R kamihime have been recorded to be drawn from gem gacha.