Cleffa you can get from the Amity Meadow Pokewalker course, breeding one from Clefairy or Clefable, or trading/migrating.
Igglybuff can also be found on the Amity Meadow Pokewalker course. You can also get one by breeding a Jigglypuff or Wigglytuff or by trading/migrating.
However, the Amity Meadow course was available only through event, so if you don't have it, do the breeding option.