I measured all of the buttons on my "old" style BGS uniforms and they are all 16mm. Both silver and gold. As Steve says, there are countless sizes and colours of buttons but you should be ok with any 16mm silver buttons you find as they can not have been BW ones. I would call the colour "Alt silber" in German terms. The buttons taper continuously to the edge. Some German BW buttons do not. Good luck in your quest.