Out of those, I think Panels built before the 90s especially are super rare and hard to find. The reason is because when they get decommissioned, taken out of service, or died completely, they get removed immediately and scrapped most of the time and not to mention it is very difficult to remove and preserve such a bulky and heavy Panel.
Finding a Working Panel from anything before the 90s is very hard to come by unfortunately. But luckily it’s not impossible.