Mayflash adapters can be bought on eBay and amazon for about $40Buy here https//wwwplayasiacom/wirelesscontrolleradapterfornintendoswitch/13/70be9Other Systems Nintendo 3DS Family;Classic > Wii Remote > Switch The Mayflash MagicNS connects PlayStation (PS3, PS4), Xbox (360, One) and Wii U (Pro) controllers to the Switch, but it also supports the Wii Remote and it's that Wii Remote support that lets you use the Classic Controller 8bitdo also makes a Wireless USB Adapter, which works in pretty much the same way
Just Found Out The Wii U Adapter Works On Switch It S Time To Get Serious About Smash Gaming