[Edric Li]

https://twitter.com/Midtiger_HK/status/1131157227291549696
https://twitter.com/arika2568/status/1122535386096340992

... and where I can I buy them?

 

[megabigeye]

The one from MIDtiger looks like a very small cable boot (probably smaller than any of the ones in that link).

The one from arika2568 just looks like a bit of heat shrink tubing.