Well, first thing's first, you can tell the rarity of your Creatu's color by clicking Creatu list in the hatchery. Any color below albino is either dye kit or gained by other means.
Seasonal eggs can only be found certain times of the year, and you're given 48 hours once you begin. You can hunt for Iluvu right now and to start you click Iluvu Egg Hunt at the top. They're found on Reiflem.