Molly sources her fabric by reclaiming unused cloth locally. The sacks come in a large size which is 10" long x 5" wide and 6" deep and holds about 6 pounds of potatoes (for example.) The small holds about 7 or 8 medium potatoes and measures 7" long x 41/2" wide and 4" deep.
You can look for Molly at the Berkeley, CA Farmers' Market and other Bay Area FM or in her shop on etsy. She is also looking into more pop-up and farmers' markets in the Bay Area. The bags run between $10-12.00 for a set of two or $40.50 for a set of nine.
PS I've just started using my pretty flowered origami sack, purchased from Molly at the SF Underground Market, but I love it already. It's handy for bulk grains and such, but also for those times when you purchase a handful of small, rolly things like radishes or figs and you don't want them to get squashed in your larger grocery bag. Even the checkout lady commented on it!
Visit Molly's website for lots more photos and enter to WIN a FREE set of origami bags!
(Image: Molly de Vries)