I will continue to update this as I find better places but here's a first draft. The numbers in brackets are the number of EVs you get from that Pokemon.
Surfing in Icirrus City - Stunfisk (2) everywhere! Seismitoad (3) can also appear in bubbling spots.
Dragonspiral Tower 1F - Mienshao (2), Druddigon (2), Golurk (2).
Victory Road 1F/3F - Banette (2), Golurk (2)
N's Castle - Druddigon (2), Zweilous (2), Excadrill (2) in dust clouds. Avoid Onix (dust clouds).
Chargestone Cave - Nosepass (1), Klink (1), Ferroseed (1). Avoid the rest (note: Boldore gives 1 Def and 1 Atk EV).
SPECIAL ATTACK spots
Celestial Tower - Litwick (1), Elgyem (1). Stick to the first floor to avoid Golbats.
SPECIAL DEFENSE spots
Surfing on Route 17 - Frillish (1), Jellicent (2) in bubbling spots.
Or possibly Route 14 - Swablu (1), Altaria (2). But a mix of a few other Pokemon to avoid.
Surfing in most places (e.g. Route 1, Wellspring Cave) yields all Basculin (2). Feebas (1) is in bubbling spots but avoid Milotic (2 Sp.Def EVs).