Catalyst
BD.org Addict
The main problem with ground walnut, as far as I know, is the sharp edges that pose a risk if your dragon does ingest any of it. An alternative loose bedding you could consider is something called bed-a-beast or eco-earth. It's been a while since I dealt with it so I'm not sure if that specific brand is around, but I used it with my girl once she was an adult without problems. It's made of coconut fibers and comes in a block. You add water to it to get it to return to a loose form and then leave it out to dry before you put it into the tank. I then put the feeding dish up on a tile so that when she was eating there was no risk of her ingesting any of the bedding (just to be on the safe side). Just another option for you to look into as you're doing your research