I may be late to the party, but I stumbled upon one of David Gruenling's websites - badassharmonica.com
Among other things the site has to offer, are biographies of many of the harp greats. He also offers a recommended discography with comments for each player.
Full access to all lessons starts at $20/month! (with annual subscription)
After watching the BluesHarmonica.com overview video, try one of the lessons below to experience a lesson at BluesHarmonica.com.