The chemical the parent comment linked is different.

NAD itself isn’t usually supplemented because it’s broken down by your digestive system. So NAD precursor supplements have been available for a while: NR and NMN specifically. These are the precursors they were talking about.

The actual drug used in this study has a different mechanism of action. It’s not directly available as a supplement, but like the parent commenter discovered you could technically find a chemical supply house to synthesize a tiny quantity of it.