I created a Yahoo answers account just for this question.
The only true case of EV trained Pokemon you will find are in the
battle frontier/tower/subway.** Every Pokemon you fight in these areas
is EV trained and has good move sets to go with it.
The person who answered this question is a hacker. I asked him.
This SHOULD answer your question pretty well. :D
EDIT: Just found out that they have a beneficial nature too, and that same guy who answered my question also told me that he thinks the EVs are:
252 HP, 252 Atk, 4 Spe (For Physically stronger Pokemons)
252 HP, 252 SpA, 4 Spe (For Specially stronger Pokemons)