in caves and mountains, especially mt. coronet
no
No.
as far as im aware the only way to get it is trade it from gts or pokemon diamond, pearl or platiunm
You can catch it at Mt. Coronet.
Clefairy's Egg Group is Fairy, so any Pokemon with the same Egg Group can breed with Clefairy, including Ditto, which has its own Egg Group.
The Pokemon clifairy does not exist. Clefairy is found in mt. coronet.
moon stone will help
You can find one with Cleffa or Clefairy (5% chance) or you can dig underground.
You have to trade a Clefairy from Leaf Green or Fire Red.
no
Clefairy is the only Pokemon in pearl that evolves with a moon stone but once you get the national dex you can evolve Jigglypuff, Nidorino, Nidorina & Skitty
Mt. Cornet.