Where do you get leftovers in Pokemon Diamond?

A wild Munchlax has about a 55% chance of holding leftovers when you catch it. You can also find a Pokemon such as Aipom, Teddiursa, Meowth, Phanpy, Zigzagoon, Linoon, Pachirisu, Ambipom, or Munchlax that has the Pickup ability. The Pickup ability is an ability that picks up random items. Once you have a Pokemon in your party that has the ability Pickup, run around places and check the Pokemon to see if it has an item attached to it every once in a while.