Actually, a simple Gram's stain, available at any hospital and almost any medical clinic with a microsope, could determine in 5 minutes whether this powder is actually bacteria, and whether it COULD be Anthrax.
Detailed testing might be needed to help establish the origin of the strain, etc.
If it is a powder composed of spores, it would not be possible to do gram stain to ID the spore. Only if you plate the organism can you positively ID via microscopy.
I have to think the US military has labs stationed in forward positions.
If not, I volunteer!