all over.
X-Plus, Marusan, M1Go = company website
Y-MSF, Marusan = Instagram
Sunguts = Twitter buried between 100s of non-release posts
Marmit = after they do a run of 50 at a festival and are no longer available under $500 and show up on auction sites
SHMA, Neca = social media
Sofvi.Tokyo does a good job pulling together press releases for some of the stylized sofubi companies, so thats a great resource, but there isn't a one stop shop that i know of