Yes, you gotta find listings, or offers, you could check places like craigslist, or wait for someone to sell one on here.
you can also commission one, though I assure you, asking for a gamecube portable is going to cost more than a wii portable, because a gamecube portable requires old parts, that are hard to find, or obsolete.
so i'd commission a wii portable instead of a gamecube, it's your money, do what you want with it, but that's just my opinion