Stun gun questions?

Are there any stores in or around LA that sells stun guns? I would like to know also how much power in it is needed. I mean if i were to buy a weak one, would it only irritate or enrage my attacker more? Or would they be able to shake it off after a few seconds? I want one that would do more than that to an attacker. Not death but enough to make them hurt and not able to retaliate