I've made a fun little project inspired by this (except it's not updated any more).

It provides easy instructions for installing old versions of packages, it takes them straight from the official nixpkgs repo.

Example: https://history.nix-packages.com/package/dotnet-sdk_3/3.1.426 (.NET SDK 3.1 actually prompted the creation of this tool, I needed it for one old project).

Each detail page provides instructions on how to install the package using nix-shell, nix-shell with shell.nix file, configuration.nix and nix-env.

The design is based on https://search.nixos.org (because I suck at graphical design).

Do let me know what you think!