PDP USB GameCube Style Fight Pad For Nintendo Switch (Various Colors) | $19-$20 | Amazon
<Whispers> It’s okay to play Super Smash Bros. with any controller you want.
But that said, I understand the appeal of the old GameCube controller design, and you can snag an extra from PDP for just $19-$20 today, in several different Nintendo character-themed designs.
These controllers are wired (via USB, not Nintendo’s proprietary connector), but they come with swappable C-sticks, so you can remove the classic yellow nub, and replace it with a stick that’s the same size as the left stick for easier smash moves.