Nix/NixOS/nixpkgs tends to hang behind git-annex packaging, which is annoying. The standalone builds of git annex work fine when downloaded manually, but that's not the nix way Here is a derivation for the standalone builds: git-annex-standalone.nix. Also this discussion.

One thing that's quite inelegant here is the lack of predictable urls for specific versions of the standalone builds. One has to grab them from the annexed content and build a sus looking download link. This also presents a bootstrapping problem as one would need git annex to do that.