Best place to find driftwood naturally wold be the nearest lake. Hemet is a nice lake out in riverside probably a 1.5 hour drive. Fish stores in south OC include The Reef, Ocean Blue, Tongs, Eye Candy, OC tropical fish warehouse, 405 tropical fish, New wave. Those are the main ones anyway.
Been to all of these.
Tongs, 405, and Eye-Candy blow away all of the rest, in terms of pricing at least. Although the others might get an odd item once in a while that is well worth checking out.