You first encounter the harvester in the case file called THE FACTS. Therefore, you must complete most of the story to even see a harvester. The guide arrow will lead you to fortune park, where a cutscene will play. You will then be required to destroy all of the harvesters in fortune park, the silver strip, and the platinum strip (the guide arrow will lead you to them). Simply kill the mercenaries guarding them and smash 'em with your weapon of choice. You cannot complete THE FACTS without destroying all the harvesters.