I believe that you are referring to the JCP sponsered Holiday Button Contest. Sephora is not sponsoring or holding a Button contest. So, it cannot be found on Sephora.com. If you received a Button pin that had a code enter it on JCP's site: www.jcp.com/christmas . If you are lucky enough to win a JCP gift card through this contest then you will be able to use it at a Sephora in JCP location but, you can't use the JCP Giftcard at a Full Sephora location or Sephora.com (FYI: you can pay with a JCP credit card on Sephora.com though).
Here's the the link to a similar question to yours that was answered on the Beauty Talk forum: http://community.sephora.com/t5/Customer-Support/Buttons/qaq-p/397469
I hope this answer was helpful =)