I dont really know how I triggered it tbh, but you get My Little Bletchley Park from Argos dropping a notebook during an encounter in the valley, then having your R&D team decrypt it. I got this on my second caring master run-through, along with the thing with Luke sending you memes and Argos messaging Asterion under his real name acting a missionary (also don't really know how I triggered those two, maybe these sub-events are RNG?) Wish I could be more help :(