They are quite rare, but I don't see why its needed to have one drop each game. The player can get full quality custom production ships without it, so its mostly a convenience item for more money and bigger player fleets.
They're needed because the endgame gameplay loop involves either endlessly babysitting colonies from expeditions + compensating for rep adjustments from expeditions or doing literally anything else while getting constant -5 rep adjustments from your overpowered defenses crushing them.
Without a pristine nanoforge, a size 6 colony can't supply it's own High Command unless it has +1 industry Admin +1 story point improvements +1 Alpha core on Industry +1 corrupted nanoforge. Since you need multiple overlapping high commands to not have to babysit colonies, that means that without a pristine nanoforge you have to import from another faction.
And, of course, pirate activity and intercepted supply shipments as well as faction hostilities reduce access... which can reduce imported space hulls... which then can create a downward spiral as defenses wear down and - by the by - you eventually can't import hulls from factions that produce hulls if you're "doing literally anything else" because they keep grinding their rep down into open warfare by raiding you for producing hulls (because murdering your best customers = profit?).
Obviously with fractional differences from lack of supply could or could not be a big deal vis a vis defenses vs raids... but that would require a calculator and brain space that I don't want to invest in a game that I'm playing to distract me from real life.
With respect, this isn't fun. This isn't even in the same galaxy as fun.