Try Kanth Sudharak Vati (कंठ सुधारक वटी) from UAP Pharma (Unjha)!!!
It works like a charm on cough, sore throat etc. It sells in most of the ayurvedic medicine shops in India. I tried a 10gm little bottle that contains mini round ayurvedic pills that taste good and work immediately. But, if you want to prepare your own, mulethi is one of the good ingredient to start with.