ftp://ftp.math.utah.edu/pub/misc
in the file dired-x.yy.tar.gz where x.yy is the current version. Other distribution formats are usually available in the same location.
That site is mirrored to several other Internet archives, so you may also be able to find it elsewhere on the Internet; try searching for the string dired at one or more of the popular Web search sites, such as
http://altavista.digital.com/ http://www.hotbot.com/ http://www.stpt.com/ http://www.yahoo.com/