I did some last summer in-house. If you'll look at
Outwater Plastics they sell a wobbler that is a spring with a self-adhesive mounting tab on each end. I had business cards printed with what the customer wanted, stuck them to one side, they distributed them and stuck them to their displays. Worked perfectly but labor intensive and they didn't really like having to use the self-adhesive tab. If I had to do them again I'd hand them a bag of springy things and a box of cards and let them do the sticking themselves. They were a pain to box once they were assembled.
Quoted them again using traditional shelf wobblers from shelfwobblers.com
(only because they came up first on Google). Didn't get the job but my price on them was cheap, about 35¢ each. Hard to beat that in-house.