As with finding the Sadhu, this requires that you explore a previously ungenerated swamp biome to find the Adivasi farmer. Also as with finding the Sadhu and with locating villages, the "chat" in the bottom-left corner of the screen will notify you once you are within a certain distance of the village. Unlike the Sadhu, however, the Adivasi farmer lives in a small village occupied by approximately one to four people; this village, unlike many others, is merely a farming village which farms turmeric and rice.
Upon locating and talking to the Adivasi farmer, he will give you one mushroom of each variety and some vines to be delivered to the Sadhu. Upon returning to the Sadhu, he will, as usual, give you 128 reputation points with the Hindi culture. After another short "meditation period," the Sadhu allows you to move onto the next quest, Exploring the Mountains.