Just northeast of Moyogalpa [1] along the “back way around the island” is the small community of San Marcos, home to a women’s group that makes and sells ceramic pieces, including authentic replicas of pre-Columbian art. Ask around in town for the taller de artesanía.
Links:
[1] http://www.moon.com/destinations/nicaragua/ometepe-and-rivas/la-isla-de-ometepe/moyogalpa