Klink was already confirmed for Gemini in Unova Horoscope, but here's 2 alternatives.
An Kanto-native counterpart to the Klink, this Twin-Bird Pokémon has two heads (plus necks) connected to a single body. Despite no visible wings, the Doduo is capable of flying. This twin bird can be considered a suitable Pokémon for Gemini sign, although not native to Unova region like Pikachu.
Another Unova-native two-headed Pokémon alongside Klink, this Snowstorm Pokémon resembles an ice-cream cone with two heads which modeled after ice-cream scoops. This Ice-type Pokémon can be another sidekick for Klink for Gemini in the Unova Horoscope.