According to Michael D’s Region 4 DVD Info Page, the Region 4 Season Six DVD set is due to be released on March 9th, 2005. Region Four is made up of Australia, New Zealand, Mexico, South America and other countries. So far, the first five seasons of M*A*S*H have been released in Region Four, with the Season Five DVD set being released on December 7th, 2004. The date is, of course, subject to change without warning.
Other M*A*S*H DVD releases already known in 2005 are the Season Eight DVD set in Region One sometime in June and the Season Five DVD set in Region Two on January 17th.
Source: MichaelDVD.com.au
