They have been releasing each season every 6 months or so. Season 8 came to DVD in March, so we should be seeing Season 9 in September or October.
It is shown in reruns occasionally on USA, but has no fixed schedule. Basically, if you want to see it, you need to get the DVDs.
It already is released, as is season 8 and 9.
JAG - 1995 People vs- SecNav 9-14 was released on: USA: 6 February 2004 Japan: 26 May 2008
JAG - 1995 Black Ops 1-17 was released on: USA: 10 April 1996 Japan: 9 February 1997
Season 1 was released to DVD on October 9, 2012. Season 2 was later released to DVD on July 9, 2013.
Season 8 will begin on Sunday, June 30, 2013
JAG Season 6 is being released May 20th 2008, the rest haven't been announced yet.
JAG - 1995 Impact 3-9 was released on: USA: 18 November 1997
JAG - 1995 The Boast 9-9 was released on: USA: 21 November 2003 Japan: 21 April 2008
JAG - 1995 Scimitar 1-9 was released on: USA: 9 December 1995 Japan: 1 December 1996
JAG - 1995 Washington Holiday 2-9 was released on: USA: 28 February 1997
JAG - 1995 Contemptuous Words 5-9 was released on: USA: 23 November 1999
JAG - 1995 Defenseless - 3.11 was released on: USA: 9 December 1997
JAG - 1995 Persian Gulf 9-16 was released on: USA: 20 February 2004 Japan: 9 June 2008
JAG - 1995 Touchdown 9-5 was released on: USA: 24 October 2003 Japan: 24 March 2008
JAG - 1995 Crash 9-15 was released on: USA: 13 February 2004 Japan: 2 June 2008
JAG - 1995 Defenseless 3-11 was released on: USA: 9 December 1997
Unfortunately, there is no season 9, :(