AP in Jackson has an unnamed source saying that Barbour plans to return to BGR Group (formerly Barbour, Griffith and Rogers), a lobbying firm that focuses primarily and Republican issues and candidates. (Their Washington DC office is actually near 13th Street NW and F Street NE, a few blocks from K Street.)
Barbour held his interest in the firm in trust while serving as governor, and reportedly continued to benefit from its activities during his eight years in office.
If true, it's not clear whether this revelation is supposed to surprise anyone, although it seems it should offer a footnote to his legacy as governor that his primary job both before and after his term is that of lobbyist.