If you surf on Rotue 227 or Route 228, then the only Pokemon you'll encounter are Poliwag (1 EV) and Poliwhirl (2 EVs).
You can also try Starly (1 EV) on Route 201.
Or there are plenty of Pokemon in the Trophy Garden: Pikachu (2 EVs), Pichu (1 EV) and Staravia (2 EVs) are fairly common, and some of the daily Pokemon give off Speed EVs too.
Route 9 is great! You get Rattata (1 EV), Raticate (2 EVs), Spearow (1 EV) and Fearow (2 EVs).