Thats the first one of those air compressors I have ever seen make it through a entire set of brushes! They usually burn out the motor long before the brushes go.
I have worked on at least a dozen or so that are built with the exact same motor and oilless compressor.
Craftsman, Camble Housefield, Black and Decker, Dewalt, Ingersoll Rand, plus the harbor freight cheapos, and likely a few others all used that base compressor and motor system at one time. They always fry the motor at some point just after the warranty is up.
So congratulations! You beat the odds! Unless of course it has a partially shorted winding that caused it to burn up the brushes. If it has low running hours on it since you bought it that would be why the brushes are burned down to nothing.
Still I would recommend tossing it and buying a real air compressor. Those high speed oilless compressors like yours are just not worth rebuilding.