I remember buying a bag of these years and years ago, and the scent lasted for a very long time. When I stored them I put them back in a zip lock bag.
One of my contacts mentioned about wanting to know how to make these, so I thought I would check online. After reading a couple articles that it would take up to 2 months to prepare I thought I would post this now.
here is one from eHow
a couple ideas here
found a different method here that takes less time