I will echo the suggestion of ReptiLinks frog scent and also note that they sell frog links as well that you could use (my westerns live the frog and the rabbit and the iguana links)
I caution using a live frog to scent as they frequently harbor their own parasites that can be passed on to the snake (like lung flukes). And yes, that includes a cheap frog bought at a pet store which is most likely a WC