Call the schools desired to check into the need to re-take the GMAT, I believe the GMAT will stand, but worth the call to double check.
I would recommend if you want the joint MBA to take 1-2 quantitative classes now to demonstrate that you have the aptitude as complemented by the GRE score (perhaps econ and finance or accounting).
In addition, the top MBA programs are likely going to want a bit more work experience, although I think the two years in foreign government will be an interesting strength in your application as opposed to the way you position it as "not business related." Top business schools look for varied backgrounds to bring multiple perspectives to the classroom.
Best of luck-
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