You can get the tech loot from normal drops, or even from the regular reward bag, but from what I understand the best chance is in the optional objective bag.
If I recall correctly, Infected space and ground drops Shield tech and PSG tech respectively, Cure Space drops the engine tech, cure ground drops weapon tech, KA space drops deflector tech and ground drops the Armor tech.
Edit:
In fact I just got a prototype borg shield tech from the regular reward bag, without completing the Infected Space optional.