One of the chapters in my LEGO Collectors Guide deals with only parts that were only sold in specific countries. This started out back in the 1950s with parts only being sold in Denmark... and some parts were only sold in Norway, others only in Sweden.. and then others only in Denmark, Norway, Sweden. Later came parts only sold in Germany, some only sold in Netherlands, others only in Italy... and (strange as it is) others only sold in Italy and Japan. Then you can add parts only sold in continental Europe, only in Britain/Ireland/Australia, others only in USA/Canada or only USA or only Canada... and finally only Japan.
Today this scenario is repeated in other countries around the world.
One of the coolest parts I've ever seen was recently shown to me by a Japanese LEGO collector.... a 4x10 trans-clear brick. These cool bricks were only found there, but their source doesn't seem to be a specific set (well not yet it doesn't)...