Hi Jim,
Here's one source that I found:
Specialty Black Garbanzo Beans at Retail Main Page
I've not purchased from them so I cannot speak for their quality or reliability. Also, the beans in the picture are almost black, much darker than the ones I bought and have seen elsewhere. However, there are ways of preparing them so that they'll have the blackish color which shouldn't change the taste or texture (AFAIK) but just the appearance of the beans. My cooked beans have a dark brown color with a subtle reddish hue. I think they turned out well, although I've no point of comparison.
Shel