I've seen gold plated square buttons around, http://www.highlandxpress.com/patterns.html#acc
But I don't recall seeing them being worn around here.

The first kilt jacket I ever got was a black argyll with the ubiquitous square chrome buttons. I took a dislike to the buttons after a while, mostly because they are ubiquitous, and being square and pointy they catch on stuff. They were held on with the little cotter pins and where easy to change, so I went to round styles just to be different. first to some round antique gold finish harp buttons as seen on the so called "Brian Boru" jackets, and currently with some round brushed silver Celtic knot styles.