Went trawling through the plural tags on Twitter today, and it turned up a resource:
This resource, originally created as a constitution for a Queer Pluralfolk union (and a manifesto for its authors), is intended for members of plural systems, their friends and aspiring friends, and others that desire to understand plurality with an open mind.
We dedicate this resource back to the community under CC-BY-SA - you may freely print, redistribute, modify, and share with appropriate credit.
I haven't read through this so I can't vouch for how good it is, but I'll leave it here in case anyone wants to take a look.
Edited to add: Some of the people who worked on this! Looks like they make a variety of neat stuff, including plural Minecraft mods. https://tech.lgbt/@sleepingdragoninn