If you were to get your hands on a QMK/VIA-powered keyboard, you could tweak the firmware for your own Fn+(anything) to map to Vol+, Vol-. Not the same, but you

If you were to get your hands on a QMK/VIA-powered keyboard, you could tweak the firmware for your own Fn+(anything) to map to Vol+, Vol-. Not the same, but you could have this 'under your fingertips' at all times. I tried this a while ago, but never used it much. I end up leaving my system volume at predictable levels most of the time, and ended up rebinding my arrow cluster's extra layer for Prev/Next song, which got much more use.