Kyoko Naka has a small Twitter list of (ex-)SGZ members:
http://twitter.com/kyochan_piano/snk-sound. There are four people on it right now: SHA-V, YAMAPY, Hideyuki Ashizawa, and then some unknown guy,
Akihiro Uchida. He doesn't have a bio or homepage link, so I have no idea who he is or what he may have worked on. I'll go out on a limb and suggest Ackey as a possibility.