Speak to Dawn's/Lucas' little sister, she will tell you about 15 different rare pokemon.
Not really that rare... in Pokemon Diamond you can find Sunkerns on Route 204
snow point temple. two rare Pokemon
Look for them in the grass
buy it at the rare Pokemon store
shiny Pokemon are rare you can find them almost any were but they are super rare
You can find the Pokemon Castform in the Trophy Garden in Pokemon Diamond, although it is a pretty rare chance.
Its a rare Pokemon in the Great Marsh.
You find Rare Candy's in Poke Balls through your adventure.
If you have a action replay, you can use it. Or if you have Pokemon pearl,you can find Palkia,if you have diamond find Dialga
You catch it in mt cornetbut its quite rare
you have to talk to the boss and he tells you what rare Pokemon you can find in his gardin
Find all locations of rare candys on serebii.net