well i know for a fact that there is a way of backing up gamecube games but you have to have your gamecube hooked up to your cpu heres a link to the thread http://forums.afterdawn.com/thread_view.cfm/61273 this has nothing to do with the above i am not advertising i am just doing this to make 2 cents per click this will be on all my posts http://www.modchip.com/clickcgi/click.cgi?goodcheats
Even if there was a modchip for the gamecube, you still can't duplicate the mini disks. They are written backwards - from the outside to the inside. A normal CD/DVD is written from the inside out. There are no consumer burners that can recreate that format. There are other ways to play backups, streaming the data from a pc to a game cube broadband adapter.
Common misconception, but they are not written outside in. Take a look at a GC disc, there is a bar code on the center track (where the index of a CD or DVD would be). I am not talking about the real obvious bar code that is on the center of the disc, this one is just outside of that, it's very thin and goes about 9/10ths of the circumference of the track. That is GC's copy protection, some sort of checksum. Stick with the streaming, it's the only way to go.
I found Directions For Instalation of a gamecube mod chip and a picture of the chip on three dif websites but i can't find outwhere to buy them!