prosing.com has tons of karaoke discs and equipment and are pretty low priced. they also are the biggest u.s. dealer. if you want the blue background with the text on the screen that changes colors as you sing you want CDG discs. If you mean actual videos with people in them and also text that changes colors you are probably out of luck--they were laser discs usually by Pioneer that fell out of vogue about 7 years ago.
a cheaper and easier solution for home/recreational use is to get .KAR files, which are midi with lyrics embedded and get a free karaoke computer program. do a search for ".KAR" or computer based karaoke and you should be able to get some info.