Thunderbolt is, arguably, the most reliable and effective electric-type move in any of the Pokemon games. It should be no surprise that most trainers looking to exploit the weaknesses of water- and flying-type pokemon would want to have one fighter with Thunderbolt. How's it found, however?
Unlike other Pokemon games, where Thunderbolt shows up a bit earlier on, Thunderbolt is a fairly late arrival to your TM collection. You'll have to wait until you've collected all eight gym badges from the Unova gym leaders, as well as made your way through the vast majority of Victory Road, before you can snag the TM. Once you reach a final chamber on the road containing blockades and rubble, heal up your pokemon...
... because your rival is about to show up. He'll approach you as you cross to leave the room and challenge you to a battle. He's no more difficult than any previous battles, as he only has four pokemon which aren't much stronger than what you'll have at that point, but it's still wise to prepare for the worst. Once you best his team, he'll hand over the TM and let you proceed to the Pokemon League.
