Not really. Maybe there’s a torrent of the source code somewhere, maybe as part of Debian or whatever. But you’d have to adjust the automatic build process to use the torrented source code. Certainly not impossible, but a pain.

If a workaround is introduced by NixOS itself, they could mirror the source code onto another Git provider, at least I saw that suggested in the discussion I stumbled across.

Side-note: I’m not from the UK myself. repo.or.cz just wasn’t reachable, from what looked like a denial of service attack or AI scrapers, that’s why I looked this up.
Although right now, I believe I can reach it fine, but get a wrong checksum for the source artifact, so hopefully they haven’t been hacked. 😵‍💫