Hi Francis,
The actual version from the course is included in the downloadable files.
But the latest version can be found here.
https://extensions.blender.org/add-ons/bone-widget/
You can drag and drop into Blender from there (or download it as well)
Plus you can actually grab this from inside Blender itself.
In the “Get Extensions” tab, just search “Bone Widget”
Let us know if you run into troubles.