You don't really need to. If you don't switch your team too much, you can just use these: http://bulbapedia.bulbagarden.net/wiki/EV-enhancing_item
to train while playing normaly. (Those items give you 4/8 ev points for any beaten pokemon) It halves your pokemon speed though, so i ussualy took it off when fighting bosses. Than you can use ev reseting items to get rid of undesirable stats while playing. That way, you only have to ev train on wild pokemons, if you have like 10-20 ev points to train left, and you want to have perfect ev trained pokemons
You can buy most ev items in sticker store