How to get a missing .drv file for a derivation from nixpkgs?

Thanks for the analysis, it is quite educational!

May I ask how did you go about deciding the specific hydra build to look at?
Also what if the package wasn’t as major as bash how would you find its details? The search at the top does not work for specific derivations. In the case of bash as luck would have it when going to any build and checking build dependencies bash comes out at the top so that was easy to find.