I too have been looking to craft or purchase a stitching clam. In French, it is known as a "Pince à Coudre". A quick google search yielded this video, hosted on Vimeo, which appears to document the manufacture of a Vergez Blanchard stitcing clam.
http://vimeo.com/22194742
After reading an earlier post about these devices being made of barrel staves, I decided to purchase a few barrel staves from a seller on eBay. I just purchased 5 made from white oak for $25 including shipping, and I plan to use them to fashion my own stitching clam. I'll post pictures when it's finished.
