We have a wire and bead Wine Glass Wrap project sheet that can be re-shaped for use as a napkin ring. (See project sheet #41.)We also can special order findings that are designed for cloth-covered napkin rings. They are pretty expensive though (over ũ if I remember correctly), due to their size, and there isn't an easy way to bead them. The minimum order is normally 1,000 pieces.
Memory wire might be a good way to go. You could bead the ring or bracelet sized memory wire, and then just wrap it around the napkin. I'm not sure which size (ring or bracelet) would be best though. What do you readers out there think?
-Polly