Lace Acuity and the surrounding areas. They give you lv. 30-35 Pokemon that include Snorunt and Snover. To my knowledge, that's the only way to get those specifice Pokemon.
You train your Pokemon to lvl 100 or you can find some at the battle frontier in the place where you rent Pokemon and select open level in Pokemon platinum
look around twinleaf, and by that i mean look in the patches of grass
Its going to be at level 47
In the safari place.
Get an Eevee and level it up in the Eterna Forest.
You get to level 77 and look in bushes.
Mount corenet (the fog level)
You have to evolve chinchar at level 14.
find a caterpie in eterna forest then level it to level 7 and it will evolve into larvitar
find a Chancey, and then get it to max friendship and level it up
you can't, you have to catch a remoraid and level it up.
You cannot catch level 100 Pokémon, but you can battle them at the battle frontier.