I'm sorry to say I know very little about the CURE TRANCE series, I've always been more interested in vocal music from I've. :/ However, I do know that there are two more volumes: Vol. 2 - Psychedelic Goa and Vol. 3 - Psychedelic IBIZA. As for availability, not too sure. You might be able to find some links by searching, or maybe try asking someone on e.g. the I've Sound Forum, I'm pretty sure someone over there might be able to help. Vol. 1 and 3 seem to be available on Amazon JP, too. I'm gonna look into it more when I have some time on my hands, you've got me interested.
(Btw, would you maybe like to share the first volume? I have never heard a single track from it and I'd really love to try it now!)