Why Can't I Find Vicks 44 Cough Syrup At Any

Why can't I find vicks 44 cough syrup at any of my drug stores. I am told they can't order it. This cough syrup is the only cough syrup that helps my cough of all the Oct syrups. My doctor ordered treason pearls but they don't work. I don't understand why when one finds something that works then it is taken off the shelves and can're be ordered.