Has anyone here come across “C Connectors” aka MIL-STD-348 ( https://en.m.wikipedia.org/wiki/C_connector / https://www.amphenolrf.com/connectors/c-type-connectors.html)

Dad has a dummy load which uses this sort of socket and I can’t find parts! They look like really chunky BNC connectors, I’m assuming from the MIL code that it’s ex-military from the US.