I've not found Tempered Lagi yet at all. I saw a reddit post saying you can guarantee Lagi spawns in the Forest if you rest at the Cliffs set to Inclemency and Morning, but it did not work for me.
Much better luck with Seregios though. I managed to save an investigation with his Dissenter as a reward. Tempered Steve is pretty difficult though.
Ah, yes, the Negotiator:
General Kenobi
<sneaky beeping>