Şu kaynakları buldum;

https://stackoverflow.com/questions/15960319/api-to-find-nearby-cities

https://stackoverflow.com/questions/15171430/in-c-sharp-is-there-anyway-to-convert-a-city-name-to-its-timezone-name-tokyo

https://stackoverflow.com/questions/13269558/find-closest-city-to-given-location