Well if you thought cheating devices were the worse things you could talk about NOW we have PIRACY!!! YAY!!!
Yes it's out there, I've come across it myself, but let's discuss why it would be a waste of a download. Firstly, a Gamecube reads mini DVDs in the REVERSE order, & it is quite difficult to burn them that way (actually I'm not sure how they do it myself as I've never looked into it). Add to that you need to "chip" your Cube to read mini DVD-Rs as it doesn't do it normally.
You do realise that it's just cheaper to BUY THE GAME rather than source some mini DVDRs (that are more expensive that normal DVDRs), buy a modchip, & risk damaging your Gamecube trying to install it?