The following literary texts explore gender-neutral pronouns:
Marge Piercy employs 'person' and 'per' in Woman on the Edge of Time - it's a fantastic read and one of my favourite novels.
June Arnold uses 'na' and 'nan' in The Cook and the Carpenter - also a really good piece of writing which highlights how dependent readers are on (grammatical) gender.
Dorothy Bryant explores 'kin' in The Kin of Ata Are Waiting for You - I haven't read it yet but it's in the post.
The author of 'Gender Neutral Pronoun Blog' adapted excerpts of Lewis Carroll’s Alice’s Adventures in Wonderland - 'ne' and 'ze' are just a few of the pronouns 'person' tries out.
This is by no means a comprehensive list so please feel free to post any other texts you know about!