u/Adam2p90

So, I think these are the best places for farming EVs. If you have any better options, I'd be happy to read them.

HP – Viridian Forest, as there are a lot of Caterpie there.

Attack – Rock Tunnel, as there are Machop there. Route 22, where there are Mankey, is also good (if you know any better places, please tell me).

Defense – Pokémon Mansion on Cinnabar Island, as there are a lot of Koffing there. Mt. Moon is also good because of the Geodude.

Special Attack – Pokémon Tower. I think it's obvious, since it's basically just Gastly.

Special Defense – Just surf on the water and you'll almost always encounter Tentacool, which is what you need.

Speed – Diglett's Cave, as there are literally nothing but Diglett there.

I hope I helped.