The legend of Zelda: Four Swords has been re-released onto the American 3DS eShop today. The game can be downloaded for free, but only for a brief four day window.
The legend of Zelda: Four Swords was released onto the handheld's eShop as part of Nintendo's 25 anniversary of the Zelda series in 2011. Since then the game has been unavailable for new 3DS owners to download.
Act quickly if you would like to secure a free copy of Four Swords on your 3DS though; the game will be removed from the shop on February 2, 2014.