The only way to get a Pichu with Volt Tackle is through breeding, and it's only available in the Pikachu/Raichu line.
You'll need 2 Pikachu/Raichu (opposite gender with each other), have one of them holding a Light Ball, then put them in the Day-Care that supports raising 2 Pokemon (games from Gen 3 onward have a Pokemon Day-Care that can take care up to 2 Pokemon, but some of those games have its feature available in the post-game).