HP: The secret base level trainer has three audinos that I find to be the most efficient, but if you are low on cash, you can take out Nidoran females and Caterpies in the Shade Forest.
Attack: Rezzai Desert, Krokorok for 2 atk and vibrava for one atk and one spd
Defense: Telnor Cave, Cubone Geodude Nosepass Onix and Roggenrola all give one Def point
Special Attack: Suntouched Exitway, Surf, Clauncher and Piplup both give one SpAtk point
Special Defence: This was a tough one, the best spot I found was surfing in metchi town. You mostly find tentacools coming in at one point each
Speed: To get a sure find every time, fish with the old rod in Midna town to find Finneons at one point each you can also fight Youngster Joey in the Memory Chamber for one point each time. This is also an ok way to make money. Route 1 can also be used as a source of speed EVs with bunnelby, ponyta, and blitzle all giving one point