Well, I assume your playing Gen 5.
If you're playing Gen 6, tag your question with 'xy'.
In fact, in all questions state what your game your playing through the tags. :)
Anyhow, Tepig cannot learn ThunderPunch through Egg Moves, unfortunately, however it can learn Superpower. So... let's learn it! :D
The Pokemon we need to viably breed with your Pignite has to be:
- In the 'Field' egg group
- Has to know the move 'SuperPower'
And there is only one Pokemon that can match this description according to my research - Nidoking.
Nidoking will always be male as well, so you don't have to worry about the gender stupidity.
Nidoking will learn SuperPower through the Move Tutor, so what I would do is since you are not training it (I assume) then trade Nidoking from another game into this game, and breed with your Pignite. Remember, it must know Superpower!
If you can't get it from another game, it doesn't seem possible to give Pignite the 'Superpower' move. However, I did minimal research so feel free to let other people answer. xD
EDIT: Thanks to my Excel-manipulating skills, I was able to find out a bunch of other Field-Pokemon that can learn Superpower through Move Tutor:
Also, some Field-Pokemon that can learn SuperPower through Level up:
So yeah. Plenty of Pokemon to choose from.
Remember to choose a male one. REMEMBER. :3
Hope I helped. :)