Simply put, no, I don't think so. At least, to do as easily/cheaply as you're hoping. A converter would probably be too expensive to be worth it. And it's still possible to do cheaply, but you'd need to mod the GC with something like a
XenoGC or something, which should allow you to force the cube to output the kind of video signal you want. But GameCubes & Wiis are so cheap it would probably be more worth it and easier (especially considering the Xeno requires disassembling your cube and soldering it in) to just find an NTSC one on Craigslist or ebay. Also, Wiis are really easy to hack, and you can install software on it that allows it to output different signals without hardware modding, if you still wanted to do that. If you're going to be playing games from SD card or USB, then you can even look for buying a broken Wii where the disc drive doesn't work (just make sure the listing says the system still boots up to the Wii Menu OK), and you should be able to easily get one for < $20.
For future reference, the thread you'd be looking for for this sort of stuff would be
this one. Though honestly even before that, Google has (almost) all the answers.
