Honestly, that specific ship has this really interesting presence because it's not super mainstream, so you kind of have to know where to look. Archive of Our Own is always my first stop; the tagging system is a lifesaver. Filter by the pairing tag, sort by kudos or hits, and you’ll find the well-known ones. I’d also recommend checking out Levi-centric collections or bookmarks from authors you like on there—sometimes people organize their faves that way.
Don't sleep on Tumblr either, even though it feels a bit old-school now. The fandom side of it is still pretty active for niche dynamics. Searching the pairing name plus 'fic rec' will pull up a lot of curated posts. I found a really tense, character-driven slow-burn through a rec list there that I wouldn't have clicked on just from the summary on AO3. It's all about following the trails readers leave.