I have no source for you, just personal experience. In my small circles (irl and online) which are not statistically significant, we usually use :
- "iel" for third person singular, used the same way as "they" in the singular form
- "ellui" also used for the third person by someone who wanted the feminin "elle" to come first
- "ol" is also used for the third person, mostly by people who want to get rid of the binary "il" and "elle" sounds of "iel"
- "elleux" for the third person plural, used the same way as "they" in its usual sense
Maybe this wikipedia page could be useful ?
Just FYI: from my experience as a native French speaker and a French resident, these neopronouns have a hard time existing outside militant and lgbtqi+ circles. Our most popular media (which are right-wing/conservative) regularly paint them as a problem, an attack on the "mothertongue" etc. and I've faced violent reactions from people I gave my pronouns to.
Kudos to you for including them in your signature !
Edit: typos.