You can find replacement shells for both, Switch and JoyCons and replacement for USB ports on AliExpress. The seller also has lots of 3DS parts, and are expanding their Switch catalogue, so maybe they will the ones you look for in future.
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UPDATE: Digitizers starts showing up [https://www.aliexpress.com/store/product/Replacement-Touch-Screen-Digitizer-Pad-Spare-Pad-W-Ribbon-For-Nintendo-Switch-LCD-Lens-Cover/1945613_32829098732.html?|eg. here.]
You can find replacement shells for both, Switch and JoyCons and replacement for USB ports on AliExpress. The seller also has lots of 3DS parts, and are expanding their Switch catalogue, so maybe they will the ones you look for in future.