It could be an old hermit who has been living in seclusion for years. This hermit has mastered the Goken and sees potential in Naruto. So, he decides to teach Naruto this powerful technique.
Maybe it's a mysterious ninja from a far - off land. This ninja travels to the Hidden Leaf Village and, after seeing Naruto's courage and determination, decides to pass on the knowledge of the Goken to him. The ninja might have his own reasons for choosing Naruto, like seeing a spark in him that reminds the ninja of his younger self.
In this fanfiction, it could be that Naruto stumbles upon a group of ancient warriors who have preserved the knowledge of the Goken. One of these warriors, impressed by Naruto's unwavering spirit, takes it upon himself to teach Naruto the Goken. This warrior would then guide Naruto through the various steps and intricacies of the technique.