The mission itself appears very early on if the 'Shen's Last Gift' DLC is installed, although you initially have to scan for a few days before you can undertake it. If the mission doesn't appear during your game then make sure the 'integrated DLC' option isn't selected! This causes SPARKs to be buildable in the Proving Ground right away, but also turns off this mission so you will be unable to complete it. IMPORTANT NOTE: If you are playing with the War of the Chosen expansion, there is an option during setup to integrate DLC into the expansion.