Special packages appear randomly while playing on a new world. Generally they are appearing in the first to weeks of a new world release.
How to buy a special package?
Special packages can be purchased in the shop view or in the event and task list.
Where are my purchased rewards?
After you successfully purchased a special package all rewards can be claimed in the event and task list (Profile -> Event and Tasks). Select the habitat, collect the reward and enjoy the benefits of your purchased package.