[Glathannus]

First of all, what constitutes a "karaoke" track?
The obvious answer would be: a non-default version of a recording, specifically without lead vocals which would otherwise be there, and without any of the other roles in the recording compensating to fill that void.

But for all I know, you could be talking about something more complicated than that. I'm vaguely aware of concepts such as synchronized lyric captions, and I have absolutely no idea where/how to find material in such a format.

If we're talking about just the audio itself, that's easy. Most Japanese artists (except Shiina Ringo) tend to release karaoke versions of their hit songs, as B-Sides.

For Shiina Ringo, there's a legitimate online-only release of the whole HF album without vocals, while everything else about those recordings remains the same (it's actually kinda neat to listen to without vocals). The Cappuccino single under Tomosaka Rie's name, also has karaoke B-Sides. Beyond that, there's nothing else from EMI.

I wouldn't be surprised if the karaoke industry took matters into their own hands and somehow fabricated their own versions of hit songs like Honnou, but I don't know how legitimate any of that would be.