No matter where you are in the world, you can catch Pokémon that are supposedly region-exclusive. You won't be able to find them in the wild, but you will be able to hatch them from eggs.
John Smith of California told Eurogamer that he caught all 145 Pokémon in his hometown of Santa Rosa or in San Francisco. He revealed that he hatched region exclusives from 10km eggs and walked around 200km to collect everything.
There were supposedly four Pokémon that could only be caught in certain regions: Taurus in North America, Mr. Mime in Europe, Farfetch'd in Japan, and Kangaskhan in Australia.
Pokémon Go features a total of 151 Pokémon, but six of them are seemingly impossible to find. No one has managed to capture the three legendary birds Articuno, Zapdos, Moltres; Ditto; or Mewtwo or Mew.