With rapid evolving items like the s club ones a third gen of the item is only released if there is a rapid evolving item bundle released containing that particular item. Rapid evolving items only ever have two generations, one that evolves and poses are added on to it. And the second gen is released fully evolved so there's no need for a third gen.
If it does get a third gen it will be released in an evolving item bundle.
For Rapid Evolving Items (REIs for short), third generations only come from REI bundles.
Once a REI bundle comes out that contains the All-Star Cheer, it will contain a 3rd gen.
For regular evolving items, the third generation comes out when the 1st generation evolves a second time.