Sorry in advance if this is a repost. If you missed the chance at The First Firewall quest, or maybe hadn't found all 4 of the DVALIN relics, or don't want to wait to until the next chance comes up to get your hands on the Simulant there looks to be a way to force the quest to start.
You simply need to find someone who has previously completed The First Firewall mission, and join their fireteam. Have them load First Firewall. Upon completion you should get the Curious Transceiver drop and proceed like normal.
I just finished doing this with a coworker who hadn't unlocked TFF quest, and it worked for us. Clutch finished all 3 warsats 2 minutes before reset too, and now he's the proud owner of a shiny new Sleeper Simulant. Hope it helps someone!