It would be very strange if the moonsugar plants weren’t also available separately in the furnishing purchase section. For instance, you can purchase the flowers and butterflies that were also in Dibella’s pack and the webs and cocoons in Mephala’s pack. These plants seem commonplace enough; it would make no sense for them to be an exception.

Edit: Actually, it seems to me very strange that these plants aren’t available already! Ideally in game, but they should have at least been in the Crown store with the release of Moonsugar Meadow. 🤔