Groundwater Vistas 5.17 Build 3 contains a working Null Space Monte Carlo procedure. This was developed by John Doherty in Pest Version 11.5. It allows you to calibrate any number of realizations based on the same base calibration. The assumption is that there are lots of parameters in the calibration (preferably pilot points) and that you used SVD-Assist for the calibration. I have tested this in GV for a synthetic 3D model using pilot points for Kx and Kz. While it is a simple model, there were over 400 pilot points and so the characteristics are fairly representative of a real model.
The next step is to work on the post-processing of the calibrated realizations and finally to incorporate this into the Monte Carlo simulation and post-processing that has been in GV for years.