It seems we do things pretty much the same way. I get my rocks and branches from the woods (damned if I'm going pay a store for something like that), although I usually clean them either by throwing them in the oven (for an hour or so) or in the sauna (about 4 hours). Wood starts burning at around 300 Celcius, but 100-150 C is more than enough to kill anything that might otherwise cause problems. Before that, I usually might let the branches dry for a month or so, which usually allows whatever insects still inhabiting it to eject themselves. Once I didn't do it, and as a result, I had a few hundred dead ants lying around the sauna.

Craft stores really are much better sources, they have much cheaper artificial plants and the plants usually look more realistic, too.