With all this talk about legendary Pokemon, there are actually several non-legendary Pokemon that are just as rare as these. Due to regional exclusivity, the following Pokemon are more difficult to find due to the regions they are restricted to.
In Europe, Tauros has proven to be as difficult to track down as any Legendary–this Pokemon is nowhere to be found.
Pokemon Go players have researched this, such a sites like Serebii and Reddit group The Silph Road. They seem to be confident, using what they’ve discovered, that that a few Pokemon are actually unable to be found in certain areas of the world.
Tauros, as mentioned above is found in North America, and it appears to be found only in this specific region. However, Tauros can hatch from 5km eggs as well.
Kangaskhan, much like Tauros, is limited one continent, Australia. However this Pokemon has been reported to spawn across the Australasia region by local fans. Kagaskhan like can also hatch from 5km eggs as well.
Mr. Mime can be found exclusively in Europe. Mr. Mime, however, is a bit more difficult to get from an egg for those in other regions. It only hatches from 10km eggs.
Farfetch’d can be found mostly in Asia in general, first being spotted in South Korea, and then in Japan. Parks and cities are the best place to look if you happen to live there. Farfetch’d can also hatch from a 5km egg.
The final Pokemon is Ditto, who is yet to be spotted in the game, although Ditto is in the game code.