There's a long running treasure hunt for some still-crated Spitfires that were supposedly shipped to Burma at the exact end of the war and then buried when no longer required.

The amount of equipment left over from WW2 was staggering.

On a slightly newer time scale there are always firearm collectors searching for something impossible to acquire now, but which might have been acquired at some point in the past and squirreled away in its factory original box in the cosmoline. Like somebody who might have purchased an imported Egyptian Maadi AKM (locally made AK47 variant) in 1982, then never unpacked it for whatever reason.

People collect these things just because, almost like pokemon cards, another example would be the rarity of finding a specific year of East German Makarov in pristine/factory new condition.

You can build a Citroën 2CV from scratch with entirely new parts - almost - because someone somewhere makes what you need.

About the only mechanical component you can't buy is the gearbox "bucket", presumably because nobody ever breaks those. You can actually get various gearbox upgrades for them which is worth it if you daily one, because the mainshaft nut can slacken off and get you jammed in gear.

I love that show