I don't believe you can. It originally dropped from the first opening of the final chest in the first mission of the cosmodrome that was added back in season 8? I think. That mission was reused as the first step of the new light quest later but I have no idea if it ever dropped the shell. I have complained for years without any response that my drop was bugged. There were actually two drops tied to opening that final chest. The generalist shell which should drop the first time and a ship which would drop on a rerun if you found 3 secrets in the final area before opening the chest. Unfortunately I found the 3 secrets on my very first run which gave me the ship and blocked me from ever getting the shell.