The special Seasonal Set Decoration items labeled "Get from [5-Star Box]" can be found only in the RED Star Boxes you get for earning five Stars in a single Hidden Object Scene (e.g. - "Mastering" the scene).

Furthermore, not every Red Star Box will contain a set item. These are quite rare, which is why they are worth so many Flowers! It isn't an easy challenge to collect all the seasonal set items, which is why they are so special. Good luck!