John Fahey is an outstanding musician and I would second that recommendation, although you should keep in mind that he travelled ALL over the map musically. Some of his more recent projects bordered on musique-concrete even. Do a little research on his discography first, but definitely dig in to it. It was, I think, Rhino that put out an excellent two-disc anthology which would be a great starting point. If you like Fahey you could even travel a little farther out on the limb by checking out Robbie Basho, another cohort of the Fahey/Kottke camp. A few other musicians that come to mind who may fit loosely within the genre(s) that Kottke resides in are Sandy Bull, Davy Graham, and Wizz Jones.