I don't know if you're in Kanto or Johto, and I've yet to set foot in Kanto, but from the games, Celadon was the place to shop. Or Goldenrod is, here.

[Customized utility belt is sounding more and more awesome... he'll store Pokeballs in one pocket. Apricorns in another.

And one for Pokedolls, just because.]