It's really hard, but you have to go to chargestone cave if it's the black version, and just walk around. But if you do happen to come across one, don't use too powerful moves on it, especially fire pledge. Also, once you come acrossone and are wondering which ball to use, use the dusk ball. Really, its not that hard, just its kind of hard to not kill it by accident, like by using too powerful moves. Lastly, use a repel or super repel. You'll have a better chance of finding a cool tynamo!!