First, what counts as "rare"? Nanoforges, synchrotron cores, blueprints, anything else?
I'm assuming we don't know what the underlying distribution is between those items, but I'd like to suggest that nanoforges (both types) and synchrotron cores are perhaps too common, and blueprints too rare.
- I consistently find nanoforges and cores in my playthroughs. I don't think I've had one (out of four, maybe five runs) where I did not have a pristine nanoforge and a core by level 45-50. And usually a couple of each, plus a half dozen or more corrupted nanoforges. The game lore implies that these should be exceedingly rare seeing as how there's otherwise only a single synchrotron core in existence and the biggest factions seem to have a nanoforge each.
- In a similar vein, the dice rolling for blueprints implies they're a bit too rare. An exploit: the loot from a raid is not calculated in advance, so if you can position yourself to be ready to raid and save the game there, you can continuously reload until you get what you want (or at least something useful). Which also means that you can derive a sense of how often things show up, and across "dozens" of raids against Culann and Chizomoztoc, I ended up with their nanoforge more often than any other rare item.