User blog comment:Unownshipper/Metallurgists Wanted: Rapture's Natural Resources/@comment-75.36.142.53-20140810065007

Its likely that the 'self-sufficiency' wasnt as perfect as Ryan desired and even after the 'cut-off' (1952 ?)  'Offical' shipments of critical materials/tools/technology (needed immediately or proven to require stockpiling) might still have been arranged long after that date.

For 'advanced' materials  plastics were becoming big in that time, and things like graphite/fiberglass were already known.