There used to be a shop called Mercado Ecologico but I think it closed down. It was a couple of blocks down from supermercado La Cadena at the end of Avenida Sarasota. The contact details were: Calle Ana Josefa Puello No. 33 in Mirador Sur, 829-435-8190,
mercado_ecologico@yahoo.com.
I moved away from the area 3 years ago, that's why my information is not up-to-date. I did drive past the other day and noticed a new health food shop opposite La Cadena, and there is also a good but pricey shop called "Organica" in Plaza Catalu?a in Piantini, on Avenida Gustavo Mej?a Ricart - but they probably don't sell fresh produce.
As someone pointed out on the thread, the main supermarkets like Nacional have a good health food section and some produce may even be organic.