I tried googling King and failed to find him saying that but came across this quote

“Let's get one thing clear right now, shall we? There is no Idea Dump, no Story Central, no Island of the Buried Bestsellers; good story ideas seem to come quite literally from nowhere, sailing at you right out of the empty sky: two previously unrelated ideas come together and make something new under the sun. Your job isn't to find these ideas but to recognize them when they show up.”