From Stillwtaers web site:

" Heavyweights: We have had some fabric issues which had to be solved before Heavyweight production could start. We hope to have some ready before the holidays, but no promises at this point. Our next batch of Black Watch Heavyweights will be made from Australian Merino Wool, you will love the fabric as much as we do. Once that is running smoothly, we will do more solid black before considering any other tartans/colors. The re-design of our standard kilts has been our main focus lately."

Don't like the sounds of that