David, I've put the question to my Facebook community, which I know includes some of the former editors of Soundzine. In the meantime, I've found that The Internet Archive, aka the Wayback Machine, does have snapshots of Soundzine at certain points in its history.
https://web.archive.org/web/20160601...soundzine.net/
(Addendum: The snapshots turn out not to be worth much, because the journal had gone on hiatus when archiving began. Rats.)
I know that's not good enough and not what you were looking for, and I hope I get some answers and better information for you.
Editing back with new news, not good. This is Charles Musser's reply on FB:
"Thanks for the interest everyone. A temporary hiatus in the publication of Soundzine turned into a permanent one some eight years ago. And then, sadly, approximately five years ago, the server supporting the archived issues suffered a meltdown and the data was permanently lost (the backup data was also corrupted). I regret that immensely and apologize to all."