Only First Queen had a commercial soundtrack release, the Duel and Duel Succession soundtracks were pack-ins with the game. There aren't any others.
Indeed the soundtracks to Kure games are brilliant. The music to Duel and Duel Succession are some of the best game soundtracks I've heard, and the First Queen series and Dark Seraphim have great music too. The games are great too! Playing through Dark Seraphim is insane and cool.
The founder of the company is still around making a web version of First Queen
http://kuresoft.net/He's had many battles with cancer but seems fine now and has updated the site a lot, though no commercial Kure games have been released for years now.