If you still need that King's Rock, there's a secret-agent lookin' guy on Rte 13 who gives you just about every specialized evolution item in the game, from Deepseascale to Protector to King's Rock. He gives a random item every day. So just save in front of him and keep asking until you get the right item. It may take up to 30 minutes just from the sheer number of different possible items.