HP - I usually use Woopers, try the south of Route 212
Attack -
Oh hell, just use Serebii. On the D/P pokedex scroll down and you can see all the pokemon who give a certain EV.
Normally i'd recommend Veekun over Serebii any day but I dont think Veekun allows you to list by EVs. Oh well.
Here's my personal recommendations, though...
HP - Wild Bidoof. Not so hard at all.
Attack - This one takes a bit of work and the Vs Seeker. East of Jubilife there's a Lass trainer - if you battle her enough times with the vs seeker, her pokemon lineup will be Bibarel and Staraptor - that's 5 attack EVs total per battle.
Defense - Iron Island. Fight everything but Golbat.
Sp. Attack - Just south of the Pokemon Manor, in the grass. Fight with Budew and Roselia.
Sp. Defense - Not so sure on this one.
Speed - Just west out of Eterna there's a pier with 4 fishermen. The second one from the right has 6 magikarp - 6 speed EVs per battle.