We do not have precomputed binvox files at 256^3 resolution for the ShapeNetCore or ShapeNetSem public data releases.
You can generate such voxelizations using the binvox (http://www.patrickmin.com/binvox/) voxelization code using the following parameters:
binvox -aw -dc -pb (for solid voxelizations)
binvox -aw -dc -pb -ri (for surface-only voxelizations)
The currently distributed voxelizations (at 128^3 resolution) were computed at 256^3 and then downsampled to 128^3 by adding the -down argument to the two commands:
binvox -aw -dc -down -pb (for solid voxelizations)
binvox -aw -dc -down -pb -ri (for surface-only voxelizations)
If you use the viewvox code to view these voxelizations please note that it requires the -ki command line argument in order to visualize the solid voxelizations.