If it's a B-side bonus track, chances are that no manufacturer has put made it available on karaoke. They, for the most part, stick to the songs that the masses hear on the radio.
Your best bet, as Mnt said, is to request the song be made for you. I think you may have better luck with Karaoke Version though, as your request will be put up and voted on. Request it with Tricerasoft too, because you never know
If the karaoke host at your venue has a player with an option called "One Touch", you can just bring in your CD and sing overtop of the all-but-muted singer, but mind you one touch isn't perfect and never will be... and words won't appear on the screen.
Hope that helps