There are not many duty free place for shopping created by the government because you already know that duty is for our inland revenue. But the government still allowed some place to be duty free for tourist attraction especially for the International tourist. Usually we can find duty free shop at Malaysia International Airport or borders.
From custom dept. website :
Duty Free Shops were established for the first time in Penang following the withdrawal of its free port status towards the end of 1977, with the aim of allowing tourists to gain access of duty free goods in the island.
At the present, Duty Free Shops are located at these premises:
International Airports such as Kuala Lumpur International Airport (KLIA) Sepang, Bayan Lepas International Airport (Pulau Pinang), Kota Kinabalu International Airport (Sabah) and Kuching International Airport (Sarawak);
Ports such as Port Klang (Selangor), Tanjung Belungkor (Johor) and Pengkalan Kubor (Kelantan);
Cities such as Kuala Lumpur, Johor Baharu, Penang, Melaka and Kuching;
Border stations such as Padang Besar (Perlis), Bukit Kayu Hitam (Kedah), Pengkalan Hulu (Perak), Rantau Panjang (Kelantan) dan Kuala Baram (Sarawak); and
Padang Besar Railway Station, Perlis.