All the large supermarkets in Santo Domingo sell the products you mention - Nacional, Carrefour, Pola, Bravo and La Cadena all have health food sections.
There are several specialised health food shops, including Org?nica in Plaza Catalunya on Gustavo Mej?a Ricart Ave. between Churchill and Lincoln Avenues, the Mercado Ec?logico in Mirador Sur (Calle Leonor Feltz), Madre Tierra in Zona Universitaria, Ananda in Gazcue, and several others dotted round the city.