I'm not entirely sure if there is a large quantity of fanfiction specifically about all the Weasley boys wanting Hermione. While the idea has potential for interesting stories, it might not be something that a huge number of fanfiction writers have focused on. There are so many other aspects of the Harry Potter world to explore in fanfiction, like new magical creatures, different timelines, or alternative endings. However, it's possible that a small number of writers have dabbled in this concept for the sake of creating a unique and perhaps controversial story.
Yes, there are likely some fanfictions out there with such a plot. Fanfiction writers often explore unique and alternative storylines, and this concept of all the Weasley boys having feelings for Hermione could be an interesting take on the Harry Potter universe. However, it may not be a very common or mainstream idea within the vast world of Harry Potter fanfiction.