You can´t, you can only get them in Pokemon Fire Red and Pokemon Leaf Green.
Entei, Raikou and Suicine are often referred to as the Legendary Beasts or Legendary Dog pokemon. They aren't in Diamond, so you'll have to trade or migrate them. You can do this from the following games: FireRed/LeafGreen, HeartGold/SoulSilver and OmegaRuby/AlphaSapphire.
the legendary Pokemon in diamond and pearl are dialga and palkia.
No, a Bidoof cannot evolve into any Legendary Pokémon in Diamond.
Heatran
a lot of legendary Pokemon
Dialga
you cant unfourtanately
arceus
you can't catch it because you already beaten the legendary
suicune is top legendary dog just play Pokemon crystal and you'll see.
no
you can't unless you have AR