The only places I'm familiar with for mp3+g downloads is CAVSUSA dot com. They mostly have THM brand available (low on my list of favs), They also have some CB and some generic CAVS brand which I'm unfamiliar with. I used to buy some of the must-have-right-away songs from them but had problems with lyrics being out of sync with the music requireing me to add or subtract a little silence from the mp3 to get them to line up. I think thay are about $2us.
You can also get them from ZOOM at Karaoke.cc (Good quality in my opinion). I've never bought any of their downloads (yet) so I can't speak to any possible pitfalls. If I'm doing my currency conversion thing right they are about $3.28us. IMO Zoom is a better brand than THM and the really nice thing about Zoom is their downloads are at 192kbs compared to CAVS's 128kbs. If I were doing mp3g I would go 192 minimum. Of course using Hoster to rip from disk using WMA audio is better quality still
Sam