I managed to find the right crystal on digikey.com you don't have to use the exact same part number, as long as you use the same value and type.
I'd consider doing this but the A/D converter alone is about the cost of a 2nd gamecube, and at this point my GC has been retired to the old 25" CRT in the living room while the Wii has taken it's spot in the home theater room. Not really worth the price of entry at this point.
I'd love to add an optical port to the Wii or the DC though