On route 212 (south of mansion) there is a collector with espeon and umbreon. I don't know where leafeon and glaceon are
Where Can I Find Leafeon, Glaceon And Umbreon In Pokemon Platinum?
You can see leafeon going south on 212 from mansion. 2 trainers you'll have to battle
Level up eevee in eterna forest to get leafeon (mossy rock is located there) and to get glaceon, level up eevee at route 217 (icy rock is located there) so I suppose those rocks have something to do with the evolution of eevee.
You get them from using different stones on eevee
You have 2 evolve 3 eevee's to get them. .
Level up Evee in forest.