Well, As Emerald is My Best Game:
SA: The Grass Next to the Volcano(I Forget its name). It's got Numels To Train SA
HP: Makuhitas in Granite Cave OR whismurs in Whishmur Cave
DEF: Granite Cave, Lower Floor, train On Arons
Speed: ANy Place with Zubats and Golbats, basically any cave...
SD: Baltoys in the desert OR Spoinks on the Volcano
Atk: Trapinchs in the desert OR ANy Place with Poochenyas/Mightyenas.