I don't where to source the aluminum columns, but my rack is built with with 1.5" diameter brushed aluminum tubes between the shelves. The top shelf has a theraded insert on the bottom side, and there is a long threaded rod that runs through all the tubes with a threaded spike at the bottom that holds it all together. The aluminum tubes have a plastic circular spacer at each end that keep them all centered on the rod.
I disassembled mine a few years ago and put foam pipe insulation inside the tubes to deaden them a bit, and then later I filled the remaining spaces with sand, which really helped.
I've been trying to find a suitable replacement for the aluminum tubes, so that I can change the shelf heights.
JD