Since I didn't make any of the meetings when Kelly Biers was interviewing members of the Peninsula Belgian American Club/Belgian Heritage Center, I don't really know if he has many Walloon language contacts outside of Wisconsin.
(When it made the TV news it caught my attention... this was the news clip: https://archive.org/details/PreservingWalloonWisconsinsLostLanguage

José or Lucien, you might want to reach out to him:

https://www.unca.edu/person/kelly-biers-ph-d/

Does anyone know more about this paper that he references? I'd read it if it was somewhat easily available, but I also suspect it might be written in French?
Colet, Eric. 1982. Le parler Wallon du Wisconsin: Aspects phonétiques, lexicaux, morphologiques et syntaxiques. Université Catholique de Louvain.