the only thing else that I can think of is waiting for the event shop to restock, getting lucky with Royal Margarine's card game, and just doing any missions that you can 💔if not, you can always try pulling for him in the standard banner when PV's update comes out in a couple of days💔 good luck tho

Have you bought his soul stones from the Raid/Boss Rush shops? I think you can get a decent amount of them from them, plus general gacha luck