i don't think ao3 *has* a tag for the light novels and as such, i don't think there's a way to find fic specifically for the light novels on ao3 (it all just falls under the anime tag, which i'm a bit frowny-faced about). i used the posting a new work function to see what came up and when searching classroom of the elite only the anime came up, and when i made a wild search for *light novel(s)* very few things came up, none of it related to COTE.