http://www.knowngoods.org/download.html contains md5sums of various freebsd, linux, osx, openbsd and solaris OS. http://www.nsrl.nist.gov/Downloads.htm contains a few CD loads of checksums (various). Not sure how to use this yet though.
http://www.knowngoods.org/ is an online service only. NSRL is still active however putting an ebuild on this would not be particulary useful. Our mirror providers would probably freak at the addition of 2G of data too.