Duck is usually eaten only in Chinese restaurants. It is not sold at usual grocery stores in Japan. There are many people who haven't eaten duck. As the others said, if we consider the aigamo as a kind of the duck, it is true that most of us have eaten duck, but aigamo isn't treated as the main dish usually. Two or three sliced pieces of aigamo are usually put on soba-noodles as garnish. Anyway it is quite difficult for you to get duck-meat at usual stores in your daily life in Japan.