BACKGROUND: Thus far I've looked at d3 examples, Highcharts, Plotly, ChartJS, GoogleCharts, Chartist, ZingChart, vis, etc.
The closest I've gotten is finding a custom software business that has this as an example of graphs they can sell you (labeled "Heat Map With Drill Through"--with the Drill Through being the graph I'd like to make-- on this page). They say they make their graphs using d3 on their site, but I'm not sure how. Maybe there's another library that works with d3 that they used and didn't specify or maybe they used d3 in a way I'm unfamiliar with. They haven't responded to my communications asking about what they did :( but at least this indicates it's possible.
Anyone have any ideas?