They might sell milk at one of those little quick shop with overpriced books and snacks within the airport, probably a pint size or something.

I am sure GCBC would supply milk for you if asked before your arrival.

Also no reason to go to carrefour for "fresh" milk, the super U in Hope Estate has refrigerated milk in the case at the end of the milk/yogurt stuff, next to the eggs. Think Rosenberg dairies or something from Florida.