Yes, there are some out there. You can start by looking on fanfiction websites like Archive of Our Own. Just search for 'Transformers Sideswipe x Prowl' and you'll likely find a variety of stories. Some might focus on their unique relationship dynamics within the Transformers universe, exploring how their personalities interact in different scenarios.
To develop the characters further, you can put them in situations that force them to change. For instance, if Fem Sam is injured in a battle, Sideswipe has to take on a more nurturing role, which is new for him. This would show a different side of his character. And Fem Sam, while recovering, could have time to reflect on her life and her place in the Autobot team, leading to personal growth.
One plot idea could be that Fem Sam discovers a hidden power within herself while on a mission with Sideswipe. They could face a new enemy that is immune to their usual combat tactics, and Fem Sam's new power becomes crucial in defeating it. For example, she might be able to communicate with ancient Transformers technology in a way no one else can.
You could also try Fanfiction.net. Although it's not as specialized as AO3 in some aspects, it still has a wide range of Transformers fanfiction. Just be aware that the tagging system might not be as precise, so you might need to do a bit more sifting through the results to find exactly what you're looking for.
Their personalities. Sunstreaker is often depicted as more vain and artistic, while Sideswipe is bold and action - oriented. This contrast creates great story potential.
One common theme is their twin bond. It's often explored in depth, showing how they support and sometimes compete with each other. Another theme is loyalty. They are usually very loyal to one another in these stories, no matter what challenges they face.
There are fanfictions where Sideswipe and Sunstreaker have to deal with a rift in their relationship. Maybe something happened that made them question their loyalty to each other. This could lead to a series of events where they gradually repair their bond while also facing external threats at the same time.
Moreover, Sideswipe and Sunstreaker are such iconic characters that having an OC in their world creates a lot of potential for interesting storylines. The OC can bring out different sides of the twins, like a more protective side when the OC is in danger. This kind of character exploration and new story possibilities is what makes these fanfictions so appealing.
Another plot could be a time - travel story. Sideswipe and Strongarm get sent back in time and have to rely on each other in a completely different era of Cybertron. This forces them to adapt and understand each other on a deeper level, which in turn sparks a romantic relationship.
You can try looking on fanfiction websites like Archive of Our Own (AO3). There's a large collection of Transformers fanfictions there, and you might be able to find some great Sideswipe x Strongarm stories.