Years ago, I contacted the Australian company (Reel Music Down Under) releasing his music, and they said the music does not exist separately. I think others have corroborated that in previous threads (you can search the FSM board).
Years later, this turns out to be untrue. The complete soundtrack appears to exist on open reels (2-inch, 16-track), and partially on 1/4" tapes. They'd need to be digitized and mixed. I inquired again with the Reel Music guy who thought perhaps the tapes didn't sound good and that's why he thought the music didnt exist.
I asked Intrada, LLL and Kritzerland a couple years ago. Intrada declined, said there were so many unknown titles in the market that it was a tough sell (although Karlin's unknown title RAVAGERS sold out). The other two labels probably aren't interested but didn't want to say it. Digitizing 16-track tapes is relatively expensive ($3000), and they would still need to be mixed. I'm surprised there is no final mixdown among his tapes.
Excerpt from an interview: Daniel Mangodt: You also performed in CHOSEN SURVIVORS. Do you often perform? Fred Karlin: That was the same period of time. I had my own studio at home and I performed quite a lot. It was very difficult at the time, much more so than now. It was all multi-track and there was no computerization to help you out, so it was quite difficult, but I loved it. http://archive.li/T1fXU#selection-703.0-622.64
Ahhh that’s a shame. It would make a great companion score to both Westworld and Futureworld. Lots of similar orchestration and electronics. Really loved the movie too. Great concept and characters.
I saw it in the cinema as a kid and it made an impression. There's some similar music in cop crime flick THE TAKE (1974), although not released either.