You can consider trading others for it in one of the trading topics of the forums.
Otherwise, it and the other roguelike Boss drops are meant to be fairly rare. Keep trying at it though! In vanilla, I spent weeks + traded 3 times for bulk quantities of Ectoplasm/Corpse Dust for Skeleton Keys after running out trying for Shar’Zul’s Worldeater. When it finally dropped, it was by far the most satisfying moment I’ve had in the game.
Side note, the Bastion runs also set me up for life on Ch’thonic Blood as well, I’ve never ran out since 