In this fanfic, Vernon might be driven by his hatred for Harry and sees the baby as an extension of that. It could lead to a tense and dangerous situation for the baby and Harry's attempts to protect it.
This fanfic could have Vernon making a desperate and evil move. Harry might have to face a moral dilemma in how to deal with Vernon. There could also be unexpected allies or complications arising from the magical world getting involved.
Perhaps Vernon Dursley sells Harry fanfic to get back at the wizarding world that he despises. He might think that by spreading false or embarrassing stories about Harry in fanfic form, he can somehow undermine the reputation of wizards. For example, he could write fanfics where Harry is shown as a bumbling fool, completely different from the real heroic Harry. However, this backfires as the wizarding world sees it as a comical attempt by a Muggle and it actually makes Harry more popular as they rally around to defend him.
In many 'Harry Potter x Vernon Dursley fanfic', the theme of growth is prevalent. Both characters can grow and learn from each other. For example, Harry might teach Vernon about the importance of acceptance, while Vernon could show Harry some aspects of the Muggle world he hadn't considered. Also, the theme of power struggle can be seen. Vernon has a certain kind of power over Harry in the Dursley household, and fanfics might explore how that power shifts as Harry grows older and more powerful in the wizarding world. And of course, there's the theme of forgiveness. Given how horribly Vernon has treated Harry in the books, some fanfics will focus on whether Harry can forgive him or not.
Redemption is also a popular theme. Writers often like to give Vernon a chance to make up for his years of mistreating Harry. They might show him gradually changing his views and actions towards Harry as he realizes the error of his ways. Another theme is the clash between the Muggle and magical cultures through Vernon's eyes. His strict adherence to Muggle normalcy makes for an interesting contrast when faced with the chaos of the magical world.
One interesting fanfiction could be about Vernon Dursley having to face a magical threat in the Muggle world on his own. He might have to rely on some of the little knowledge he has about the wizarding world through Harry. Another could be a story where Vernon and Harry are forced to work together during a crisis that affects both the Muggle and wizarding communities, changing their relationship completely. There could also be a fanfiction exploring Vernon's past and how it might have influenced his treatment of Harry, and then how things could have been different if certain events in his past were changed.
One interesting fanfiction could be about Vernon Dursley's perspective during the time when Harry first received his Hogwarts letter. It might explore his extreme reactions and the inner turmoil he felt at the thought of magic being real. Another could focus on a situation where Vernon has to interact with the wizarding world in an unexpected way, like when he accidentally stumbles into Diagon Alley.
Most of the Harry Potter fanfics that touch on Vernon Dursley's comeuppance are more about him being made to understand how wrong he was. In some stories, magic might be used to make him experience the fear and isolation that Harry felt in his house. For instance, he could be magically trapped in a small space, similar to how Harry was locked in his cupboard, which gives him a taste of his own medicine. But again, this is not torture in the cruelest sense but more of a moral lesson.
Well, I don't have a specific 'Harry Potter x Vernon Dursley fanfic' on hand, but you could start by looking for tags related to both characters on fanfic platforms. Some fanfics might focus on how Vernon Dursley's view of Harry changes over time, or how their interactions impact the overall story in new and unique scenarios.
Many in the wizarding community would probably be very critical. Fanfic is often a passion project for fans, and Vernon's motives of just making money from it would be seen as wrong. They might organize to stop him from selling the fanfic. On the other hand, there could be a few who are curious about what a Muggle like Vernon thinks about Harry and the wizarding world through his fanfics, so they might buy them just to see what's inside, but still be ready to condemn his actions.
There might be some out there, but it's a rather unusual pairing considering Vernon's often cruel treatment of Harry in the original series. Fanfiction can take all sorts of creative turns, though. You could try searching on popular fanfiction websites like Archive of Our Own or Fanfiction.net. However, this pairing goes against the typical relationship dynamic presented in the Potter books.
Another theme is family. Since they are related, albeit reluctantly in the original story, fanfictions often explore what it means to be family. They might show how Harry and Vernon could form a strange but real family bond.