Most big supermarkets like Auchan and Carrefour have them, as well as most of those smaller supermarkets in the basements of big shopping centers like Wangfujing and Ito Yokado. Chinese name is 青柠檬 which just means “Green Lemon”, but they are limes.
Those basement supermarkets are the best for strange and exotic produce. The Ito Yokado one even has avocados… for like 50快/斤 🙁
I have been Yokado and Carrefour many times but never seen lime, i think green lemon still lemon they are not lime. Lime is smaller and different smell, i know that green lemon you talking about, yes it is easy see anywhere, i have been check QingShiQiao food market but didn’t find out lime, maybe i should go 驷马桥 fruit market to take a look. 😛