You can try fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'Kakashi finds baby Naruto' on their search bars, and you'll likely find some relevant fanfictions.
One popular plot is Kakashi taking on a father - like role. He might train Naruto from a very young age, using his own unique skills and knowledge. This often leads to Naruto growing up even more powerful and having a closer bond with Kakashi than in the original series.
Kakashi would likely be very concerned. He would immediately assess Naruto's injuries. If they were serious, he would use his medical skills to start treating him right away. His first reaction would be to make sure Naruto was stable and out of immediate danger.
Kakashi might immediately offer a comforting presence. He could put his hand on Naruto's shoulder and just be there silently, letting Naruto know he's not alone.
One idea could be that the baby is from a hidden clan. Naruto decides to protect the baby from those who would use its special abilities. He takes the baby under his wing and trains it as it grows up, passing on his ninja values.
Kakashi would approach Naruto's pranks with a mix of discipline and love. For instance, if Naruto tries to scribble on the walls, Kakashi would stop him gently. He'd then sit Naruto down and show him where he can draw instead, like on a piece of paper. He'd also tell Naruto stories about how important it is to respect their home. When Naruto does something really naughty, like trying to pull the cat's tail, Kakashi would firmly say 'No' but then immediately follow it up with a hug. He wants Naruto to learn right from wrong but also wants to make sure Naruto knows he is loved no matter what.
Well, Kakashi is a complex character. When he discovers Naruto is abused in the fanfiction, he may first feel a deep sense of guilt for not noticing earlier. He'd then use his skills and influence in the village. He could start by reporting it to the proper authorities in Konoha, like the Hokage. And at the same time, he'd be there for Naruto, providing emotional support, talking to him, and helping him through the trauma. Kakashi has his own past traumas, so he'd understand what Naruto is going through on some level.
He'd probably be a mix of angry and sad. Angry at whoever or whatever caused Naruto to be in this state, and sad because he cares about Naruto so much. He might clench his fists tightly, trying to control his emotions while he focuses on helping Naruto. He'd also feel a sense of guilt, wondering if he could have prevented this from happening.
One possible plot could be that Naruto was on a mission alone and got ambushed by a group of rogue ninjas. Kakashi, while out on his own patrol, stumbles upon the injured Naruto. He quickly takes Naruto to a safe place and uses his medical ninjutsu to stabilize him. Then, he might start to investigate who attacked Naruto and why, leading to a revenge - based sub - plot or uncovering a larger conspiracy against Konoha.
Kakashi would become more nurturing. In the original, he was a teacher, but as an adoptive father, he'd have to be more affectionate. He might show his face more often to Naruto, as a sign of trust, and be more open about his emotions.