I think if your really concerned abut the ethical treatment of badgers you just shouldn't shave with a natural bristle brush. Its really that simple. I would take a claim from any commercial operation that the animal was treated humanly with a grain of salt.
The fact is the badger is a pretty ferocious creature. If you've ever cornered one you know what I mean. A spooked badger can force a Grisley Bear to back down so no wild badger is going down without a fight.