Blender Commander is a Blender plugin, and it's just used for exporting 3D models made in Blender to WCP/SO format.
The MAT files come from data.tre, so, if you don't have any MAT files, you'll have to extract them from data.tre using HCl's treman utility.
If you've installed the OpenGL patch, there may be some MAT files in the mat folder under your WCP/SO directory. Those files can be loaded in the MAT viewer as well.