Gather from Rosevan island, it becomes a trade pack after.

Also found in the Secret Cave in Southeastern Serendia. You can be shown its locations from a quest out of Glish Inn. You need 5 corn flour to complete it. The cave has lots of sapphire, silver, and a few emerald and topaz mining nodes along with wild herbs and the Autumn Bellflower. Get a light source before and get ready to jump and fail to get to 'secret' areas.