Don’t know if this is of any interest, but usually we’re talking about wanting sound deadeners in the DM room. I know we need “approved” solutions, so I don’t know if these qualify, or are of any interest to anyone.
http://www.homasote.com/products/440-soundbarrier
https://dallas.craigslist.org/ftw/zip/d/15-pcs-2-2-homasote-board/6337052426.html