The pentatonic kalimba is a great instrument for jamming and improvising, because no matter what you do, it always sounds wonderful. At last, there is a great book for learning technique on the Hugh Tracey 11-Note Pentatonic Kalimba.
75 exercises in 48 pages, B/W photos, CD included.
The first half of this book covers G major, and the second half of the book covers G minor, which you can tune to yourself. See additional images for example pages from the book.