Starting with Sunny Side Cay, released for Easter in July 2016, some egg series have become location-specific. That’s why there are some series that are aren’t available to unlock in the main Hatchlings game (Location: Upstate New Yolk). To unlock these series, you’ll have to wait until you have an opportunity to travel to the native hunting location for these series. You'll know if a series is in a travel location if it has an airplane icon when you view it on your basket profile.
Watch for the travel icon in your game to know when you can visit other Hatchlings destinations.