Hello,
WP is free to download and try for 14 days, but regardless, it will not be able to remove a certain instrument. It would be an extremally complicated thing for any piece of software to complete.
If the harmonica parts were prominent anough (read - loud) you could put it through an applicaiton like Twelve Keys and it "might" pick it out of the track for you by playing with the gain settings.
Have you tried looking for the paper music for that track?