September 29, 2006 (Open Season), September 24, 2008 (Open Season 2), October 21, 2010 (Open Season 3), and January 3, 2012 (Another Open Season).
Only Seasons 1, 2 and 3 have been released on DVD. It is currently unknown if the remaining seasons will be released.
Presuming you mean released on DVD, as of 02|2013, Seasons 1 through 15 & 20.
The Hoobs - 2001 Seasons 1-15 was released on: USA: February 2001
As of December 2008 all seasons (1-5) of I Dream of Jeannie have been released to DVD. All seasons are available separately or in a complete boxed set.
Seasons 1 and 2 of Zorro will be released on DVD on November 6, 2009.
The Four Seasons - 1984 The Loan 1-5 was released on: USA: 4 March 1984
Prime 9 - 2009 Hitting Seasons 1-6 was released on: USA: 2009
The Four Seasons - 1984 The Doctor Is Out 1-12 was released on: USA: 10 June 1984
The Four Seasons - 1984 The Matchbreaker 1-10 was released on: USA: 20 May 1984
Prime 9 - 2009 Pitching Seasons 1-4 was released on: USA: 2009
The Challenge Battle of the Seasons Aftershow - 2012 Aftershow 1-1 was released on: USA: 10 October 2012
The Four Seasons - 1984 Living Dangerously 1-6 was released on: USA: 11 March 1984