You can start by looking on popular fanfiction websites like FanFiction.net or Archive of Our Own (AO3). Just use the search function and type in 'Harry Saves Vernon' and you should get a list of relevant fanfics.
Another idea for a 'Harry Saves Vernon' fanfic could be set during a time when the wizarding world is under attack and the protection spells around the Dursleys' house fail. Harry, who has a sense of duty towards his aunt and uncle despite their past treatment of him, comes back to save Vernon from the invading dark forces. He might use his Patronus charm to drive away Dementors or use defensive spells to fend off Death Eaters who are targeting the Muggles in Little Whinging.
Perhaps Dudley finally stands up to his father's cruel treatment of Harry. Maybe he realizes that Vernon's behavior towards Harry is wrong and uses his own physical strength or some clever ruse to get Harry out of a difficult situation Vernon has put him in.
In this type of fanfiction, Snape could simply intimidate Vernon. Snape has an air of mystery and a certain power about him. He might show up at Vernon's doorstep, give Vernon a cold stare, and with his reputation as a powerful wizard, Vernon might be too scared to oppose him. Snape could then just take Harry without much resistance from Vernon.
In this fan fiction scenario, Snape might use his knowledge of the Muggle world and Vernon's weaknesses. Snape could have found out some information about Vernon's business affairs or personal secrets. Then he blackmails Vernon into leaving Harry alone. By doing this, he effectively saves Harry from Vernon without having to use too much magic and draw unwanted attention.
Obviously, Harry Vernon is a main character. But often, there are other characters created specifically for the fanfic or borrowed from the original source material if it's related to a known franchise. For example, if it's in a magical - themed fanfic, there could be a wise old wizard who guides Harry Vernon on his journey. Or a young sidekick who accompanies him in his adventures.
This is a very disturbing and inappropriate topic. Fanfic should not involve such non - consensual and immoral content. There are many positive and ethical fanfics in the Harry Potter fandom that focus on friendship, adventure, and character growth.
Well, it depends on how you define 'good'. There could be some out there. Fanfic writers are very creative and might have come up with scenarios where Vernon has a change of heart and develops some sort of positive feeling towards Harry. But you'll have to dig through a lot of fanfic to find the really great ones. It could involve Vernon seeing Harry in a new light, like realizing his courage or something like that.
One good Harry Vernon fanfic could be 'Harry Vernon's Magical Adventure'. It might involve Harry Vernon going on a journey through a magical realm filled with unique creatures and challenges. Another could be 'The Secret of Harry Vernon' which perhaps uncovers some hidden aspect of his character or family history. There could also be 'Harry Vernon and the Lost Artifact' where he embarks on a quest to find a powerful and ancient item.