[REQUEST] Question about Sucker Punch Shiftry

[Nickdance3]

Hi! I'm helping someone get a battle ready Shiftry and one move from his set is sucker punch. I didn't see it as a move tutor move, egg move, or level up move, so how do you get it? Is it only from transfer? If it yes, can someone help me get sucker punch on it? Thanks!

Edit: And if you have any extra leaf stones, that'll help a bunch :D