Parent company Heroic Publishing has ceased publishing three times in its history. First from early 1989 to late 1990. Second, and most lengthy, from early 1994 to 2003. Third from late 2007 to early 2009.
As such, #1-4 of this series were published from 2006 - 2007, while #5 was published in 2009.
Issues published since 2009 are published print-on-demand as Heroic Publishing no longer meets Diamond's minimum threshold for distribution.