We present a method for the determination of the local concentrations of interstitial and substitutional Mn atoms and As antisite defects in GaMnAs. The method relies on the sensitivity of the structure factors of weak reflections to the concentrations and locations of these minority constituents. High spatial resolution is obtained by combining structure factor measurement and x-ray analysis in a transmission electron microscope. We demonstrate the prevalence of interstitials with As nearest neighbors in as-grown layers.