There are a lot of Japanese Music Libraries that can be previewed from a website.
There are a lot of that cannot.
I think those that cannot be previewed anywhere online are some of the rarest ones to even find. Not all of them, for example, the Teichiku BGM Library used to have previews on YT, they got deleted, and you can still find some of those for sale online.
Music libraries such as U-PHONIC, Arcal, The Roland MusicBase series, original Sound Bank and Nash Music Library CDs, etcetera, are very hard to find these days, as far as I've seen.