The locations are in the cortex surface (field Vertices):
https://neuroimage.usc.edu/brainstorm/Tutorials/ExploreAnatomy#On_the_hard_drive:_Surface
The values at surface level are in the source file (field ImageGridAmp, if you selected the advanced option "Full sources"):
https://neuroimage.usc.edu/brainstorm/Tutorials/SourceEstimation#On_the_hard_drive
The values re-interpolated in the cube must be recomputed explicitly (eg. with the menu "Export as 4D matrix")