I would be interested in what you find.
We found a source of wood shavings and sawdust, we could take as much as we wanted for nothing, but it was a mixture of Oak (ok), Walnut (may be a bit strong, not sure of the mix ratio) and Tulipwood (?).
Not having any guarantee of how the wood had been handled, treated etc, we took it all down the dump.
At least with "smoking dust" you know the sawdust is food grade.