Fresh ginkgo has become more rare over the years (pronounced baht guo in Cantonese). They usually are available in the frozen section of Asian markets, but the taste of those are far inferior to fresh nuts. As has been posted, when the fall comes around, you may see more older ladies/gents hawking small bags of them on the street in Chinatown. They're usually harvested locally (literally in the local parks, gardens, etc wherever ginkgo trees are found) and taste great. When I was very young, we never had to buy ginkgo nuts, because my mom would make us all go harvesting for gingko nuts in Brookline. If you're adventurous and don't mind getting a little smelly, it's something you can easily do in the fall too.