Since 3.45.x, there are no tarball releases. To get the source for a release version, use the corresponding git tag, or download a tarball at https://gitlab.gnome.org/GNOME/gnome-terminal/-/archive/TAG/gnome-terminal-TAG.tar.bz2 replacing TAG with the desired tag's name (e.g. 3.40.0). Older releases are still available here.