The SOM approach was developed by Teuvo Kohonen, and his group developed a C++ implementation called SOM_PAK that is downloadable here. I then use SOMAnalyst to prepare the outputs for ArcGIS, where I create the visualizations.

I have Matlab scripts that implement the process from start to finish from .csv input. They’re a subset of the scripts available in the TextVisToolbox (TVT) I co-created to make topic modeling and text visualization easier. That has a lot of stuff you wouldn’t really need though, so email me if you’d like the subset used for this analysis. To run the scripts you will need Matlab running in a OSX (or Unix) environment, as well as ArcGIS and a compatible version of Python.