Pucks are sold individually.
I originally installed Woodcraft Bar End Sliders after having bent a set of handlebars in a simple lowside crash. In a recent similar incident, I am certain that the sliders saved my handlebars... and my race weekend. The pucks are designed to be easily replaceable, and are like inexpensive insurance for more expensive parts of your bike!
I have gone threw a few of these now. (I fall a lot haha…) They work great and are very easy to swap out.