There are some creams available in Watsons in Hong Kong. They're a pit pricesy (3-500 dollars). I'm not sure if those work, but I'm thinking of giving it a try!!!
Try carboxy treatment. That is what my doctor recommended as having the best effect for old stretch marks-- but it takes about 10 treatments to see any marked difference. It is common in Thailand but I don't know if there are people in HK that do this.