Perhaps you are thinking of the Rasta Farm? It is on the right hand side of the road from Cole Bay to Marigot - look for an open gate and a large Jamaican flag(?), follow the road through the field until you reach the buildings. Closed Saturdays. What they have depends on what is ready to harvest.

There also a couple of fruit/veg stands in Marigot market, but mostly fruit and spices (no green veg).