You can either get it by:
- A chance to get it from universe chest which you can get from Ares Event (Saturday 2pm) or from running the AEU instance (rarely run on this server)
- Buy from someone else
Or Boutique Item (Endless) Universe Chest for 2 Gold.
The chances are as follows:
- (40% chance) 5x Revelation Potion (For spotting players who are in Stealth Mode, but is temporary and has a cooldown timer after)
- (20% chance) 4x Apocalypse Page
- (19% chance) 4x Chrono Page
- (21% chance) 1x Random AEU Skill book
Since the chance on getting a book is fairly random, it's better to ask World Chat if someone's selling it.
Good luck