This website might be useful for you:
http://www.asia-planet.net/korea/major-shopping.htm
Korean department stores usually have sales in each of the four seasons. Generally, each department store has a two-week long sale period in January, April, July and October. It is a good idea to check out the advertisements and details of these sales on the Internet. You can also contact the KNTO Korea Travel Phone +82-2-1330 to learn the exact date for the sale periods. However, be prepared to battle the crowd in the department stores during these sale seasons.
