Yeah, there is an rsync endpoint for the whole /files/ tree 
rsync rsync://www.quaddicted.com:26123/public
The singleplayer maps/mods are physically located in https://www.quaddicted.com/files/by-sha256/ nowadays to avoid filename collisions. All other places of those files (/filebase/, /files/maps/singleplayer/) are just symlinks. So if you want to grab just those:
rsync -avP rsync://www.quaddicted.com:26123/public/by-sha256 directory_on_your_system
That directory is ~35GB at the moment. Feel welcome update your clone regularly, this has virtually no impact on the server. In the future this is planned to grow substantially because I want to integrate all kinds of files into the archive.
To get a more usable file tree from it, you could move all the files into one directory, but there will be at least one duplicate filename already and many more in the future.