The one I linked above is the ONLY CALC() polyfill that I could find, and as I mentioned it’s no longer curated and doesn’t seem to work. I’m not very familiar with Modernizr though and it seems to (perhaps unnecessarily) rely on it so that could be part of the problem.
The StackOverflow link you mentioned is one that I’ve seen – and it’s great for allowing me to quickly build cross-browser support in via prefixes, but won’t actually provide CALC() functionality to IE. I’m using CALC() in this fashion to craft gutters between each column. The more common approach to this is to use an interior container and fashion the gutters that way.
I suppose for IE8 I could just remove the gutters though… wouldn’t be as pretty or a very elegant solution but it would work.