Easiest place to find these are crystal isles. There are often beached tuso on the ocean surfaces near the dessert area of the map. Tame a turtle, hit the tuso once while mounted when it pulls you off and is still grabbing your turtle go near it's mouth between the tentacles and feed it black pearls (it will eat 50 pearls everytime) When it releases your turtle just rinse and repeat until it's tamed. I recommend either put full points in health for the turtle or bring a healer (snow owl/daedon) and heal it when its low.