Berries are not able to be grown in-game in Gen V; they were to be grown in the Dream World, a virtual world that is now inaccessible. As a result, berries can't actually be grown in Gen V and the EV-reducing berries can only be obtained at the following places:
- Join Avenue, from the Flower Shop.
- Route 5, from a Pokemon Breeder who sells berries. (Tamato Berries cannot be obtained through this method).
- Black Tower/White Treehollow, as the reward for completing the boss trainers of Area 10.
Hope I helped. :)
Sources: Bulbapedia's respective pages on each of the berries; the respective pages of the locations, source