www.StillwaterKilts.com in Minneapolis sells these. The tartan is a machine-washable acrylic that does a very good worsted wool imitation.
Their sales are mostly limited to eBay, but after I got my Royal Stewart at auction, I e-mailed them and ordered another of their kilts in Black Watch directly. Both cost the princely sum of $75.00 (+ shipping) each. I had to do a little work on the buckle pins on the Black Watch (the points were a bit on the "sharp" side), but the rest was VERY good, and my Royal Stewart is PERFECT. I haven't seen anything else even close for the money, and am quite pleased with them.

Just the view from here! - Dakotan