Most common & useful Umbreon EV spread: 252 HP, 252 Sp. Def, 4 Def.
This is if your Umbreon is bred to have Wish. I think a walling is the best role for an Umbreon, but if you don't have Wish, I'm not inventive enough to come up with an offensive set for Umbreon (which it is not particularly suited to).
EV enchaning items - lists the locations of all the EV boosting braces. You can get the Power Weight in Route 4 (in W2), and the Power Band on Route 13 (W2)/ Plasma Frigate (B2). All the braces are available at the PWT or the Battle Subway.