Yeah, it's one of the more practically relevant downsides of not really switching to metric. It could start with mandating metric-based norms for building part

Yeah, it's one of the more practically relevant downsides of not really switching to metric. It could start with mandating metric-based norms for building parts in new designs for federally-funded construction, as well as mandating in consumer protection regulation that the metric measurements have to be no less prominent than non-metric units (well, technically that'd be about SI units). At some point potentially requiring operations with large-enough warehouses to offer the metric-norm equivalents for parts according to non-metric legacy norms, if they reach some threshold with inventory turnover on those parts where it'd not be a big burden to also offer those metric equivalents. But yeah, I know the feeling of foreign norm components being hard to get, from when I tried to get the screws used for consumer-grade camera tripod mounts. They are iirc 1/4" machine screws. Roughly like M6, but far from compatible.