UPDATE.

Just caught Zekrom, now I'm after Thunderun!
I hunt you down, I will.

Also, to any one who is still near the beginning of the game: I never needed an Electric pokemon until the 6th Badge oor so, and the cave you got through to reach the 6th gym has joltiks, the spider, and the one I got, tynamo, which evoles into this guy.

You make him evolve into eelektross via a thunderstone.
Recommend you wait until after 44, so it learns thunderbolt.