Relicanth is tough to find in Pokemon GO, along with a few other newer Pokemon
Not every Pokemon in Pokemon GO can be easily encountered. The latest example of this is Relicanth, who players have only found in Fiji, New Caledonia and Vanatu, as well as New Zealand thus far. If you want to catch this Pokemon, it seems you’ll need to be by the Pacific Island region.
There are four other recently-added Pokemon that could be a bit difficult to find as well, though they aren’t quite as limited as Relicanth. Plusle and Zangoose have been spotted in western parts of North America, the Arabian peninsula, and a few African countries. Minun and Seviper have been located in Australia, a few Middle Eastern countries, and several island nations in Europe.