Pre-tabbed Midis?

I've seen a handful of midi files that are already set up to play right hand/left hand, but not many. Aside from Synthesia's store, I also havent seen much in the realm of paying for pre-tabbed songs. Is this because the fingering is difficult to save to the midi? I have edited several of the songs myself, but I am having trouble finding the time these days. Is there a person(s) or website that offers this?