Excuse me, I don't know where there is specific information about buying moon cake coupons in Songnan, Baoshan District, Shanghai. However, I understand that the recycling and trading of mooncake coupons may involve some specific markets and trading channels. It is suggested that you inquire in the following ways:

1. On social networks, such as WeChat, QQ, etc. Search for keywords such as "Songnan mooncake coupon recycling" or "Songnan mooncake coupon trading", and you may find some information about related businesses or private vendors.

2. On some second-hand trading platforms, such as idle fish, turning around, etc. Searching for keywords such as "Songnan recycling moon cake coupons" or "Songnan moon cake coupon trading" may also find some relevant information.

3. In addition, you can also consult the nearby mooncake coupon sales point or supermarket and ask them if they can recycle mooncake coupons or know where there is a recycling point.

It should be noted that when trading mooncake coupons, we must pay attention to legality and security to avoid fraud or other risks. At the same time, the market and price of mooncake coupons will also be affected by many factors, including market supply and demand, brand, quality, face value and so on. Therefore, we must know the market before trading and carefully evaluate the price.