I forgot to add where I get info. For me it started here with Fishraider, and it remains one of the best sources. A lot of guys still have and use dads or grandads gear, especially in Blackfish circles.
Online auction sites, look for adds like Wanted to buy, best prices paid. These guys are collectors and dealers, they really know they’re stuff.
Otherwise general online searches for brands and models will lead to other forums both local and international, guys like us who love their fishing. eg. Butterworth rods or Alvey reels turning up in England or NZ .
In a lot cases there isn’t much info out there, but I am still surprised how much research leads back here to Fishraider. I search images too as a bit of a shortcut.