The list of all old gitorious repositories as well as their actual content is now available as the gitorious valhalla, maintained by Archiveteam. We should inject all those repositories into Software Heritage.
It's not a lot of content (~120K Git repositories).
Here is what they say to people interested in mirroring:
Please don't try to mirror the contents of this web server. It's 5 terabytes (after deduplication!) and the storage is slow at the moment. If you'd like to copy the data out, please email first and we can arrange something better for everyone.
The contact email address is: firstname.lastname@example.org