While this is by no means a fan-produced cover, I’ve just encountered something fairly interesting. Frontwing apparently made some sort of… school festival simulation/dating sim game called Time Leap Paradise. Anyways long story short, you can get the girls in the game to perform a song for the school festival and two of the choices are Tori no Uta and Little Busters…
Needless to say, these covers are pretty damn good. The characters are voiced by some pretty well-known VN seiyuu’s (one notable is Yui Sakakibara). But yeah here are some examples:
They’re even wearing the uniforms!