watermelon juice [Western Nassau County]
are you looking for it as an ingredient or a beverage? many mexican places will carry aguas frescas or fresh fruit drinks. ideally a sandia (watermelon) agua fresca is nothing more than blended watermelon, maybe with a little sugar depending on the melon/maker. sorry i cant give you tips on where exactly to look, but if you have a local taqueria/mexican market its worth checking it out.