I have bought sets from https://typemachina.com/collections/keysets. They used to be called Originative but changed the name at some point. Keysets can be really really expensive. Like $125 you wait months for that is essentially plastic but it’s made in a specific factory in Germany lol But, there are lots of cheap sets too. mechanicalkeyboards.com is another place that should have more affordable sets. Just make sure you choose the right layout and get the correct amount of keys for your board. There are artisans too and you can spend lots of money on a single key that is a piece of art.

Shokz is a brand that makes them. I haven’t had a pair but a student of mine had them and liked them.