This isn't standalone, and doesn't have press-for-mute, but the DasKeyboard 4 Pro has a nice, large aluminum volume knob (and a separate mute button near it).

This isn't standalone, and doesn't have press-for-mute, but the DasKeyboard 4 Pro has a nice, large aluminum volume knob (and a separate mute button near it). Works perfectly in Linux, along with the "sleep" button. It's part of the keyboard so it's close to your hands and doesn't have any separate cabling.