I think the last release was when [Github cancelled uploads](https://github.blog/2012-12-12-goodbye-uploads/).
Geany-themes is packaged in the [Win32](https://download.geany.org/geany-1.35_setup.exe) and [MacOS](https://github.com/geany/geany-osx) releases and I think most Linux distros are packaging it for their repos.
If you just want an archive, in Github you can [download the zip file](https://github.com/geany/geany-themes/archive/master.zip).