I train in the meleemelee meadow against oricorio for 2 speed. I also train at night on rout 10 against aridos for 2 attack. And golbats in the vast poni canyon for 2 speed.
If you use adrenaline orbs to get the sos, the second Pokemon to come in as help is always worth double the EVs. So bring along a Pokemon with false swipe.
Plus with the ev bands you get from the battle royale, every sos Pokemon is worth 19-20 evs, depending on their base ev drops.
