This is a FAQ Mr. Anonymous. I suggest you do a forum search for "instructional" or something like that.

Here are two sites that specialize in instructional audio and video tapes. They both will send catalogs if you request them: Homespun Tapes and Stefan Grossman's Workship

Stefan Grossman is an expert on Delta Blues. Homespun Tapes offers lessons by Rory Block who I think is one of the best modern interpreter of Delta Blues.

Good Luck with a great subject.

Murray