Training tomes are one of the possible rewards when using the scrying stones in those rainbow hued lights in places such as Thundering Steppes, Nektulos, Enchanted Lands, etc.
Buy scrying stones for 10s a piece at the docks in Thundering Steppes (from a Ratonga behind some crates on the West wall of the first house on the left as you enter the docks) or Nektulos (from a Dwarf by some crates on the right hand side just at you come off the long pier after zoning in from TS).
So get a few stones and look for the strange lights on the ground. Take care, though - you might disturb some sleeping monster or other. Good luck.
More specific information can be found on the official forum.