Blue Tome, is now loot of Ghazbaran but in the past was be reward from Demon Legs Quest (Now Demon Helmet Quest).
Green Tome, in the past could be obtained on Isle Of The Mists, in a respawn.
Grey tome, in the past could be obtained on Mintwallin, in a respawn.
Purple Tome, i now loot of Orshabaal, Angry Demon, Demon, Rage Squid and Vexclaw. Also is part of reward of Purple Tome Quest.
Red Tome, is now loot of Ferumbras, Morgaroth, Infernalist and Warlock.
All tomes can be gifted by CipSoft or Oficcial Fansites in their contests. But this dont have real use, just decoration.