My wife is in Iraq for our anniversary.  Which flowers will hold the
best inside a box for me to mail to her?  Where can I get them and how
should I package them?

Possibly orchids.  For sure, silk flowers, and I am pretty sure she
would understand why they aren't live flowers and appreciate your
gesture just as much.  And when she brings them home, I expect they
will remain a reminder thereof.

I second Myoarin's idea of silk flowers.