Instructions
Visit a video game store. These stores accept trade-ins on games and hardware, so they may have some limited edition GameCube controllers that are not out on display.
Check on the Nintendo site to see their current hardware selections. Their site gives you an idea of what limited edition controllers are available for sale. You may be able to purchase certain models directly from the company.
Bid on controllers on an auction site. As long as the controllers are in good condition, they can prove to be a valuable buy.
Join a gamer's community. A gamer's forum can put you in touch with other GameCube players. They can give you information on finding controllers or perhaps you can work out a trade deal if they have a controller that you desire.
Look on other online sites that provide items for sale. You may be able to find some gamers looking to sell their limited edition GameCube controllers under the "For Sale" section of the classifieds.