The one thing with the glass-bushing caps is that almost every single one was full of PCBs, hence their tendency to disappear if any work had to be done on poles with these units mounted. Edit: Looks like these were PCB units, given the sign under the light.

That fire reminds me of a couple lost historical buildings out here - the Hanson Building fire here in town over Memorial weekend 1991 (there were two nice antique malls on the main floor - Cottage Oak and Three & Co. - both yielded good insulators over the years; I remember being in the back upstairs half and noticing it seeing just a bit warm for May...) and the recent collapse of the Schamber's building in Freeman (the last owner only cared about the new addition out back; the original part was so badly neglected the building should've been condemned long before the wall gave out).

That explains why these bushings are very rare to find on poles and not something I'd expect to see at a show or antique shop.