Welcome to hell.

This is the hardest soundtrack to obtain: it requires extracting files from a Cave Story+ Switch update. The process is long and complicated, and it's been so long since I've done it that I honestly can't remember the steps.

I recall that it involves decrypting a standard CS+ Switch installation package, combining it with the update package, and then extracting its contents. These packages come as '.nsp' files, and can be dumped from a hacked Nintendo Switch.

Because it involves decryption, this process also requires that you obtain the 'title keys' to CS+ and its update data.

I think SciresM's 'hactool' is one of the tools you'll need to do this:
https://github.com/SciresM/hactool/

When that's all done, extract the contents of the 'data/base/ogg_ridic' folder into this folder.