Mirroring github repo with nested repositories

I am trying to add a version of a github repo, link locally to one of my projects. The github repo contains a forked version of another repo, so a nested repo inside the original.

How do I go about doing this? I have tried with mirroring and remote add upstream but this results in not pulling the nested repos. I essentially just want it forked locally so I can add my own small changes, not to make a PR but just for me and my purposes.