Free berries are available daily form the Berry Master, and from the Flower shop in Floaroma Town where you may also find the Sprayduck key item for watering berries.
You also get one free Berry every 24 hours from a lady in a house in Pastoria City. It's the house directly left of the Pokémon Center. It's always a Type-Resist Berry. Also, in Platinum version only, you can purchase Berries at $20 each from the Market on the basement floor of the Veilstone Department Store. However, only five Berries are ever available (as far as I'm aware):
Figy Berry
Wiki Berry
Mago Berry
Aguav Berry
Iapapa Berry
Also, just for completion's sake:
Girl in Pick a Peck of Colors Flower Shop can give the following Berries:
Cheri Berry, Chesto Berry, Pecha Berry, Rawst Berry, Aspear Berry, Leppa Berry, Oran Berry, Persim Berry, Lum Berry, Sitrus Berry
Berry Master can give the following Berries:
Cheri Berry, Chesto Berry, Pecha Berry, Rawst Berry, Aspear Berry, Leppa Berry, Oran Berry, Persim Berry, Lum Berry, Sitrus Berry, Figy Berry, Wiki Berry, Mago Berry, Aguav Berry, Iapapa Berry, Razz Berry, Bluk Berry, Nanab Berry, Wepear Berry, Pinap Berry, Pomeg Berry, Kelpsy Berry, Qualot Berry, Hondew Berry, Grepa Berry, Tamato Berry, Cornn Berry, Magost Berry, Rabuta Berry, Nomel Berry
Woman in houst next to Pokémon Center can give the following Berries:
Occa Berry, Passho Berry, Wacan Berry, Rindo Berry, Yachi Berry, Chople Berry, Kebia Berry, Shuca Berry, Coba Berry, Payapa Berry, Tanga Berry, Charti Berry, Kasib Berry, Haban Berry, Colbur Berry, Babiri Berry, Chilan Berry
(I know BK's guide tells us this as well, but it'd be easier to view which berries you can get this way).