This post is just a link to the resources you’d need to sew your own zafu. I have a sudden hankering to try this out, and maybe you do, too!
Two sites with instructions* on how to do it (in case one disappears (impermanence and all that)).
Source for Kapok and/or Buckwheat filling: http://www.zafu.net/buckwheat.html
Update 8/31/16: Before my retreat, I used some material (from the timer bags) and sewed the zafu cover. When I got back, the Kapok had come from Carolina Morning and Lucy helped me stuff the zafu, which was a little crazier than I’d expected – that stuff is seriously fluffy!!!
*The instructions above and illustrations were originally published by John Daishin Buksbazen in a book called “To Forget the Self: An Illustrated Guide to Zen Meditation.”