The mic he is using is a Shure Green Bulllit one of the old standards for playing blues. If you can Cup it well it give you a distorted harmonica sound, loved by many. But…its heavy and big. The new ones are from Mexico and dont have a very good element. You can find some more good sounding Blues harmonica mic’s, just Google the net.
I disagree with Joe (sorry Joe ;-)) the mic Joe is talking about is a great harmonica mic for a Clean harmonica sound (Fiddle tunes etc.) but not for Blues.
I don’t now how much experience you have with amplified harmonica, if not, a good recommendation is to purchase a Bottle of Blues harmonica, you will be surprised how it will sound if you Cup it tight.
Good Luck finding a good mic,
Have Fun, John