For starters, I usually recommend "Music for Bondage Performance 2" on Extreme. I'm not sure if that's still in print though. Used to be pretty easy to order. It's not quite as ambient as the first and there are quite a few tracks, most in the 4-7 minute range, as opposed to the 1 74 minute track or 2-3 20+ minute tracks you find on some Merzbow releases. I think "Amlux" is his latest and as such there's a good chance that it is most similar to what you heard at Tonic. I've never heard "Amlux" myself but I've read many positive reviews on the Net. "Pulse Demon" is pretty good and should still be available. Actually, you can download "Pulse Demon" (in addition to "Venerology", "Tauromachine" and a couple others) in it's entirety from emusic.com if you sign up for their 14 day free trial. I haven't seen many Merzbow MP3 on the file-sharing networks (Kazaa, Gnutella, etc).