Fight everybody in the riolu event and a cherim will be there
it evolves into cherim
You can't catch cherrim in pearl, but cherubis are almost everwhere. It evolves at lv 21.
Either Cherim or Munchlax
You cannot 'find' a cherim in Pokemon Diamond. You must first catch a Cherubi, and then level it up to where it can evolve into a Cherim.
I belive that you slather honey on a sweet smelling tree, just as if you where looking for a munchlax.
You have to evolve Cherubi at level 25. It isn't posseble to find a wild Cherim, you wil have to catch a Cherubi by spreading honey on a tree and come back for it later while the tree is shacking, or you could just get Cherim by trading in the Global Trade Center.
in Pokemon diamond go to iron island and find a camper trainer and fight her
By catching Cherubi from honey trees, and leveling it up to level 25.
you do not find dialga in Pokemon pearl
A trainer owns a Cherrim by the Pal Park in the grass at the end of the route, near some ground where berries can be planted. Hold off on killing it so that it can use Sunny Day, which shows its other form.
Trade with Pokemon Pearl or Pokemon Platinum
the best Pokemon you can catch in Pokemon pearl is heatran