To put it quite bluntly, they don’t seem to exist.
Very little fantasy or even science fiction seems to address or even acknowledge the idea of gender-neutral pronouns or terms of address. I have seen a few instances in stories that present angels as masculine, feminine, or neuter, using “he” “she” or “se” (pronounced “SEH”). However, in most speculative fiction, the gender binary of male/female or masculine/feminine predominates. I understand why; English just doesn’t have a good system for addressing neutral genders. The only thing we have is “it” which is dehumanizing when applied in a social context. People I know who identify as gender neutral refer to themselves as “they” (which is a little awkward and confusing to me) or they use masculine pronouns because in English, when a gender is unknown, the masculine tends to be the default. I love Japanese honorifics because they can convey titles and respect without being tied to gender most of the time. I can also understand why a lot of older fantasy doesn’t go beyond two genders because authors and audiences either didn’t know about it or didn’t accept it; anything outside heterosexual relationships or traditional gender roles wasn’t readily acknowledged. (The first time I saw a homosexual character featured in print was in 2005 when I read the short story “Lord John and the Succubus” by Diana Gabaldon. I have yet to read a story featuring a gender neutral, asexual, or trans character,)
Luckily, we’re growing up a bit as a society and it would be nice to see the spectrum of gender and sexual identity recognized in fiction.