So the design was originally by PowerA, but they no longer sell that model. So you could try their support team, but its unlikely they will have spares for sale.

The new manufacturer is listed as BD&A, but they dont have a website, and the only other place selling the charger is some canadian retailer.

So I would check with Nintendo support to see if they have a lead.

Edit: per amazon reviews, PowerA never actually sold replacement clips; it might be better to just ditch the charger and go with something non-proprietary.

https://www.amazon.com/PowerA-Joy-Pro-Controller-Charging-Dock/dp/B075FF6HDN?th=1