It's generally bad practice to include a song instrumental with a cover UST. It's better for there to be a readme with a link to where to obtain the instrumental officially. In some cases, it may even have to be purchased. Support the people who make the songs.
What @Kiyoteru said. You should always support the original artist in any way you legally can or else... there may be no more songs to cover. Nothing stopping disgruntled producers (who aren't seeing their work being valued) from pulling the plug on covers, remakes, etc. cause they get/got sick of people not paying for the off-vocal.
Haha, don't worry ^=^ To find utau covers of a song, it helps to search for the song and add utau to it, be it on SoundCloud, YouTube, and if that doesn't work try NicoNico
Haha, don't worry ^=^ To find utau covers of a song, it helps to search for the song and add utau to it, be it on SoundCloud, YouTube, and if that doesn't work try NicoNico