It's an active spy mission, meaning you need to have a spy in that city. It's a somewhat costly mission, so you may not see it if you're not really pushing your espionage. I believe it's called Ferment City Revolt though I'm probably wrong. Check your Espionage Screen, and it'll show you all the operations you can do against that leader, and it'll show you the cost to do so. If you don't have EP equal to or greater than the amount needed to preform the Op, then it wont appear.