I just checked on Ebay, and found this, the elastic set mentioned above:

http://cgi.ebay.com/ENGLISH-WOOL-SET...item230d3c3d44

Many of the shooting socks on Ebay, British made, come with matching garters. For example, the sock and turnover might be one colour, but the toe, heel, and a stripe on the turnover a contasting colour; the garters incorporating both colours:

http://cgi.ebay.com/Traditional-Engl...item5f764fa595