The Walking Dead Season 3 premiered in October 2012 and had 16 episodes, ending on March 31, 2013. No Season 3 DVD release date has been issued yet (we'll update when AMC releases intel), but we can guess based on past dates.
Season 1 only had six episodes, starting in October 2010 and ending in December of 2010, and its DVD set was released on March 8, 2011. Season 2 had 13 episodes, starting in October and ending in March 2012, and the DVDs were released on August 28, 2012.
Since Season 3 pretty closely matches Season 2, except for the three extra episodes, we're going to throw down the guess that the DVDs will be released in late August/early September, not too long before the October 2013 premiere of The Walking Dead Season 4. But that’s just a guess. Stay tuned for details, and hope for some really cool extras!