You get the talisman of the north by using the other 3 (the 2 you found and the talisman of the south) in the correct order at a statue in the middle of the derelict tunnels, which has +2 Wisdom, 3 enchantment slots and a couple other random bonuses (
Talismans).
There are 3 crystals that can be found around Maxos temple, which when placed in the 3 dragon statues (where the imp ZixZax the almost wise is) cause a chest to appear with random loot. IIRC they may be called dragon treasure by name or in the description. If not, I'm not sure what you mean.