There's a mirror of it at the obvious place[1], with instructions on how to contribute in the header. This took me the time it took to type in the URL as a gue

There's a mirror of it at the obvious place[1], with instructions on how to contribute in the header. This took me the time it took to type in the URL as a guess. "wordpress github", "wordpress source" both have this as the first result. [1]: https://github.com/wordpress/wordpress https://github.com/wordpress/wordpress