Tyranny of Dragons and Underdark quests

The drop rate of the books required to get the boons is ridiculous I have 80 lvl Characters who are still trying to get the first book required in Tyranny of Dragons despite having done loads of the required quests same goes for the Shores of Turin and Underdark skirmishes. It is so frustrating at each boon must be done in order so even if you have the later books your still stuck.