Hi,
I did some digging and I couldn't find the OST you're after for download but if you really want it so bad, given no one has uploaded after all these years (publicly) then you may want to consider buy it from Play-Asia (
https://www.play-asia.com/thatrical-feature-gegege-no-kitaro-nihon-bakuretsu-original-soun/13/703d03) as it is in stock. Not really expensive, to be honest but I'm not a fan nor ever heard of this series, personally.
However, I hope this may help you. I found the Original Soundtrack Vol. 2 (
Thread 222700) and posted it for you.
Take care. :)
Edit: Here's another upload - Best ~Youkai Kayou Shuu~ (
Thread 222705).