You can try looking for it in local bookstores that specialize in Japanese manga or anime - related novels. Sometimes they carry imported novels like this.
One way could be through a kekkei genkai transfer jutsu. If a powerful ninja, perhaps an old hermit with knowledge of ancient jutsus, decides to transfer Sasuke's Sharingan to Naruto for the greater good of the village. This jutsu might be risky but in the world of fanfiction, anything is possible.
In some fanfictions, it could be due to a special jutsu gone wrong. Maybe a jutsu that Kakashi was using to transfer some of his chakra to Naruto for a mission accidentally transferred his Sharingan power as well.
Well, 'Sasuke Shinden' is likely to be about Sasuke's story. It might cover his growth, his new adventures, his relationships with other characters, and his development as a ninja. It could also explore his inner thoughts and how he views the world around him after all his experiences.
In some fanfictions, Naruto gets the Sharingan as a gift from a dying Uchiha. This Uchiha, realizing Naruto's importance in uniting the ninja world, gives him the Sharingan. Naruto then uses it to understand the Uchiha's pain better and tries to bridge the gap between the Uchiha and the rest of the village. He also has to train hard to master the different levels of the Sharingan, like the Mangekyo Sharingan which comes with its own set of risks and rewards.
The 'Sasuke Shinden' light novel mainly focuses on Sasuke's adventures and his journey after leaving Konoha. It delves into his growth, the challenges he faces, and his relationships with other characters from the Naruto universe. It might include his encounters with new enemies and his continuous pursuit of power and knowledge to protect his village and loved ones.
Well, from what I know, the Naruto Shinden novels often expand on the existing storylines. They could be about the new generation of ninjas in Konoha, their training, and how they are influenced by the older generation like Naruto. Maybe some novels center around a specific character other than Naruto, such as Sasuke's solo missions and what he discovers during those travels. It's also possible that they explore the political situation in the ninja world after all the major battles have been fought.
Well, Sasuke is the central figure. Other characters from the Naruto universe who are related to Sasuke's story could be included. For example, Sakura, who has a special relationship with Sasuke. And maybe some characters from the Uchiha clan who play a role in Sasuke's journey in the novel.
The 'sasuke shinden full novel' could potentially revolve around Sasuke's solo missions. It might detail his struggles, the new jutsus he develops, and how he deals with the various threats and challenges that come his way while being away from the main group. Also, it could explore his inner thoughts regarding his comrades and his role in the ninja world.