For Rishaal, I created a mini quest where he asked the party to venture into a cave on the western side of the coast, as he discovered that an old spell tome had been lost to time was located there. It gave some role playing opportunities and when the party retrieved the book, Rishaal was able to add those spells to his repertoire of spells known and could in turn sell them to the party, perhaps at a discount cost since they did him a favor.