For the 4th anniversary snack, players could obtain two Pikmin of each color.
Players in Japan and Taiwan can obtain seeds not just through challenges but from FamilyMart convenience stores.
Note that you can’t acquire seeds from the same store again until 72 hours have passed. However, major terminal stations in Tokyo have such vast numbers of stores that this shouldn’t be a problem.
The image shows a map view of the area around “Ikebukuro,” the third busiest terminal station in the world in terms of passenger volume.
On the other hand, players in rural areas complain that “there’s no FamilyMart nearby,” and I imagine players outside Japan and Taiwan will find obtaining these silver seeds particularly challenging this time around.