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.
You might try looking on major online bookstores like Amazon. They often have a wide range of manga available, including Nana.
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.
The best chapter pointer here is Chapter 1, "I'm Not Interested in Uncultured Men". It opens with Jiang Li, I'm warning you, don't set your sights on Yinwan anymore, or... and closes on Yet before she had the chance to teach her a lesson, the male lead arrived....
Chapter 3 is the strongest chapter-level answer because it starts from Qiao was still annoyed at the attitude of this unknown girl when she heard... and follows through on Jiang Yan, forced into a marriage with someone he did not love, had....
Chapter 873, "The Sooner, The Better", is the clearest early answer because it turns Shuiyun Temple's situation into a concrete plot event. The chapter gives readers a real answer by opening on Under a curse?!" Wan Jia stood up excitedly.
Chapter 858, "If You Dare, Take It", is the clearest early answer because it turns Qixing Tower's situation into a concrete plot event. The chapter turns that into something concrete by moving from Changqing flicked his horsetail whisk, face wooden, and said,...
Chapter 915, "Take out 1 million!", is the clearest early answer because it turns Meng Xuezhi's situation into a concrete plot event. The chapter gives readers a real answer by opening on Hong Pei's expression was very unpleasant. and ending on How can you just randomly insult someone?.
Look to Chapter 37 for the clearest answer. It begins with The barrage was suddenly filled with hahas, but the two guests present..., keeps building through He Yun spent most of her time filming movies, had no interest in variety..., and lands on I look forward to your guidance." He Yun nodded.
The best chapter pointer here is Chapter 20, "Miss Su, your defense is somewhat clumsy". It opens with Several people turned their heads upon hearing the sound and saw three... and closes on So, he turned and questioned Jiang Li..
Chapter 929, "Award Ceremony", is the clearest early answer because the buildup finally cashes out in a real clash. Early on, The Golden Statue Award is considered the most prestigious award in.... By the end, With 7 billion at the box office, you've already made history." Shao....
If you want the clearest chapter reference, go to Chapter 5. Early on, Actually, when Manager Fang saw Jiang Li, he was somewhat surprised.; later, the chapter leans on Because she was really too beautiful, and very young, completely different....
A practical answer is Chapter 3, because it turns the idea into a concrete scene. The chapter opens with Qiao was still annoyed at the attitude of this unknown girl when she heard..., adds pressure through So without a second thought, she blurted out a fierce challenge, "Fine, if..., and ends on.