I'd suggest checking out specialized comic book stores. Some of them have imported manga and could have the Nana box set in English. Also, don't forget to search on eBay; sometimes you can find rare or hard-to-find items there.
You might try looking on major online bookstores like Amazon. They often have a wide range of manga available, including Nana.
You could start your search at local libraries. Sometimes they have manga collections and might have the Nana box set in English. Another option is to look for fan forums or communities related to manga. People there might be able to point you in the right direction or even have suggestions for specific sellers who offer it.
Chapter 669, "My First Love Sister Who Died Young", is the clearest early answer because it turns Chen Qijun's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Bang," the door closed, but Chen Qijun's words lingered in Tai Fan's...
Chapter 643, "Jiang Li Dominates the Trending Searches!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. It opens with Qi Tianyu joyously carried his construction to the side to wait for...
Chapter 826, "Deadlock", is the clearest early answer because the violence around Shuiyun Temple becomes final instead of hypothetical.
Chapter 896, "Are You a Male Model?", is the clearest early answer because it turns Wen Jiaojiao's situation into a concrete plot event. The chapter turns that into something concrete by moving from Upon hearing this, Wen Jiaojiao seemed to think of something and...
Chapter 606, "Are There Crocodiles?!", is the clearest early answer because it turns Mouse Game's situation into a concrete plot event.
Chapter 543, "Please Name Ten Things You Dislike About Su Yinwan", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. It opens with What did Jiang Li just say? and closes on No, how dare this guy try to seduce Jiang Li?.
Chapter 644, "Has Shang Shaojing Actually Gone Bankrupt?!", is the clearest early answer because it turns Has Shang Shaojing's situation into a concrete plot event. It opens with Su Yinwan was already on her way home when she saw the trending...
Chapter 662, "No Mirror, Is the Urine Matte?", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. Early on, Ji Yanbai and Mu Ye exchanged a glance and then began searching their....
Chapter 557, "Where Did This Rotten Fish Come From, It's Disgusting", is the clearest early answer because it turns Guo Xing's situation into a concrete plot event. The chapter gives readers a real answer by opening on The triple broth was almost done, Jiang Li dusted her hands off and...
Chapter 617, "Moral Kidnapping? No Such Thing!", is the clearest early answer because it turns Su Yinwan's situation into a concrete plot event. Early on, The cabin wasn't far from the lake, just around fifty meters away.. By the end, Knock on the door, I can't hold on much longer." [?.