Here's Issue 11, which I think was the last issue. I'd love some of the earlier issues, but they are pretty rare and are little out of my price range by the looks of things - http://brickbatbooks.blogspot.com/2008/08/new-arrivals-source-music-of-avant.html .
For more on the magazine see wikipedia http://en.wikipedia.org/wiki/Source:_Music_of_the_Avant_Garde
There's also a CD of a lot of the artists featured: http://www.pogus.com/21050.html
To see what some of Issue 7/8 looked like, check out the previous post: