Rare Enchanted Books with better Entchantment Levels

Pretty rare enchanted books with entchantments, that exceed the normal level you can get from trading or entchanting. These books would be found in dungeon chest something similar and would have entchantments like sharpness 6 or 7. To make it harder these book could be guarded by the Warden, so you would have a reason to go find him, they would also be a good reason to go exloring the underground. 

(Sorry, for grammar or spelling mistakes english is not my native language)