When the first Star Wars film was made things were just thrown away. Construction workers were finding props in dumpsters and would bring them home as souvenirs. That's the only way many of those pieces survived, as the movie prop collecting hobby didn't really exist at that time except for a few pioneers.
For instance there were sixty Storm trooper helmets made for the first movie, but only six are known to exist and that includes those owned by George Lucas. They've been lost forever, unless a few of those construction workers have them up in the attic!
The helmets created for the third film can be found, but there is a slight difference from those first ones, so know the difference and be informed if you see one for sale.
Note: Image is of a Storm trooper helmet from the first Star Wars movie. This was purchased from Christie's Auction within the last few years for just under $40,000.
Source: Jeff Castillo, ScreenUsed.com
