This iTunes visualizer was originally developed by Graham Cox of Apptree software. Graham has let his website's domain registration expire, and doesn't plan to continue updating or supporting this project. Thankfully, before the domain expired, he kindly open sourced the plugin's code.
I downloaded a copy of the code, and have uploaded it here for archival purposes. This project is currently not maintained, but if you want to hack on it, please feel free. If you would like to be the maintainer of this project, please get in touch with me.
Note: I am not a macOS developer, so I will not be able to help resolve issues. That said, please feel free to open issues for other people to help with.