What I do is use a file sharing program and do a search for instrumental songs or karoake . but alot of the times they dot usually include the lyrics . Windows media player can search down lyrics for you but so far ive only seen it find one or two sucessfully .
English songs are just too hard to find. In terms of karaoke, it never took off, and they always did some odd CD+G stuff. And on top of that the songs are usualy midi sequenced or something.
I usually listen to Chinese though, which isn't a problem since you can get Karaoke VCD Tracks. Instead of Dual Language, they just use Dual music/vocal tracks during the Music Videos (lyrics are already in the videos). Also, because its really popular, you get the musical score from the original company like Virgin, Sony, BMG, ect rather than some homemade sequenced midi stuff (Generic branded music LOL). I guess VCDs are more universal too. Works on DVDs, Sega Saturns, PCs, or basicly any VCD player.