Just searching google I came across this book.
The Confederate Army 1861-65: South Carolina & Mississippi by Ron Field.

Of several Scottish Charleston companies the oldest was the Union Light Infantry, formed at the Carolina Coffee house in 1807. Named in the honor of the union of Scotland with England in 1707, this "Lowland" corps maintained a Scottish style of dress throughout its existence. A vetern writing to the New York Scottish American Journal in 1870 commented that its pre-war uniform included "the tartan plaid and pants and bonnet of the [British Army's] 42nd Highlanders, and gilt thistle buttons on their coats." Another company, called the Highland Guard, was established during 1857. Still in existence on the eve of the Civil War, this unit wore a full highland uniform even closer to that of the 42nd (Highland) Regt: a bearskin bonnet with red plume, scarlet doublet with dark blue facings, and kilt of black and green Government sett ("Black Watch" tartan).
Google books will only let me look at certain pages, I can't see much more about this.