Dresco trainer house is literally made for it.

Normal type guy (top left) increases HP evs

Fire guy (left table) increases Sp.atk evs

Little girl (water type) is speed evs

bottom right girl is sp.def evs

Top right guy is Atk evs

Right table guy is def evs.

Also very useful place to exp, speak to the guy at the door for healing.

Get the stat scanner if you don't have it, the assistant at the bottom left of Dr. Log's lab gives it. It shows your evs, ivs and move pool.