The note from Blackbird is a paper note in Fallout 4.
Location[]
It can be found on Agent Blackbird's body at a radiant location when Butcher's Bill 2 has been started.
Transcript[]
Augusta overrun. Two coursers, unknown number of old-models. I'm the only survivor. They came straight at us, knew our location. Package's fate is unknown. If I don't make it out, make them pay.
-BB