Yes, there are likely 'Bardock Kills Frieza' fanfics out there. The Dragon Ball universe has a huge fan base, and many fans like to create alternative storylines. You can try searching on fanfic websites like FanFiction.net or Archive of Our Own.
A plotline could start with Frieza hearing about Broly's power and being jealous. He then devises a plan to ambush Broly. But Broly, being extremely perceptive in his own way, senses Frieza's approach and is ready for the fight. As the fight progresses, Frieza realizes that Broly is much stronger than he expected and has to use all his dirty tricks to try and win. Or perhaps the plotline could involve Broly being captured by Frieza's forces, and then Broly breaks free and goes on a rampage against Frieza and his minions.
In many fanfics, Broly would likely win. Broly is known for his extreme power and near - uncontrollable rage which gives him a huge strength boost. Frieza, while powerful, has been shown to be outmatched by the likes of Goku and Vegeta. And Broly is often depicted as even more powerful than them in some fan interpretations. So, in a one - on - one fight in a fanfic, Broly has a good chance of coming out on top.
The plot could start with Bardock having a premonition of Frieza's future actions against the Saiyans even before the destruction of Planet Vegeta. He then secretly trains and discovers a new form or power that allows him to stand up to Frieza. When Frieza arrives to destroy the Saiyans, Bardock reveals his newfound strength and battles Frieza. After a long and intense fight, Bardock manages to defeat and kill Frieza, changing the course of the Dragon Ball universe. This could also lead to new alliances and power struggles among the remaining characters.
There's also the possibility that it was an accident involving a time - traveling character. Perhaps someone from the future came back in time and accidentally caused Frieza's pregnancy through some unforeseen interaction. This would open up a whole can of worms in terms of time - travel paradoxes and how it affects the future of the 'Dragon Ball' universe.
There are fanfictions where Vegeta has a spiritual awakening of some sort. He realizes his true potential and his connection to the Saiyan pride. This newfound power allows him to generate a massive energy field around Frieza. The energy field then compresses in on Frieza, crushing him from all sides until he is completely destroyed. This method not only shows Vegeta's power but also his growth on a more spiritual level.
Another strong opponent could be Hit. Hit has the ability to manipulate time with his time - skip technique. This would give him an edge against Broly. Broly's brute strength might not be enough when Hit can literally disappear and reappear at will, striking at Broly's weak points during his time - skips.
Issei could be one of Broly's potential friends. Issei is known for his friendly and outgoing nature. He might be intrigued by Broly's power and want to befriend him. Also, Asia could be a friend. She has a kind heart and might reach out to Broly, who could be seen as an outcast due to his strength and different background. Her kindness could break through to Broly.
Broly's sad tale is a complex one. He was a Saiyan with incredible potential, but his own people rejected him. The Saiyans were afraid of his power and banished him to a dangerous planet. Growing up in isolation, he developed a violent and angry nature. His only connection to his past was his hatred for Goku, which was kind of misdirected. This hatred drove him to constantly seek revenge, but really it was all because he was so alone and mistreated as a child. He was a victim of his own people's fear and jealousy.
Since Broly has a rather wild and untamed personality, Naruto could learn to be more in touch with his primal instincts. This doesn't mean Naruto would become a brute, but rather he could find a new balance between his kind - hearted nature and a more aggressive side when necessary. For example, in negotiations or battles, Naruto could be more intimidating. Also, Broly's loyalty to his own beliefs (even if they are sometimes extreme) could inspire Naruto to be more firm in his own ninja way.