Check out aquabid.com. They sell driftwood, not sure about rocks. Also, you could check out a garden nursery center or landscaping company for rocks you'd want. There's a place that is near where I live, and they sell all sorts of inert rocks that are generally for lawn landscaping or for fish ponds, but I was able to buy a few larger rounded stones for a few dollars. I've noticed that fish stores normally don't have great selection in rocks or driftwood pieces.