Pretty sure there isn't a way around killing the giant rat and saving the dragon early on. That should have given you the water fang if memory serves.

Unless you leveled up to the 80s and killed the dragon....

Also I don't think Unei's speach actually has a type of algorithim or method to it. ie... if you cheated somehow through the game and had no fangs.... unei would still say you had only one to go.

I'm not sure how you missed the fang of water. That one seems kinda hard to miss.