Purchase it from the Windy Bee Egg shop after donating Cloud Vials to the Wind Shrine
Donate Cloud Vials to the Wind Shrine to increase your favor with Spirit Bear
Complete Spirit Bear quests to unlock access to the Windy Bee Egg
Obtain it as a rare reward from the Wind Shrine after making large donations
Buy it during special limited-time events if it is available in the shop
Receive it from quest rewards or event rewards when offered