I used one last summer to trade a GC to a store I never could find anything in, and it worked great. I had another to trade after Christmas, but it looks like the site I used doesn't exist anymore, and all the other sites I found while browsing around looked super shady.
You could always try Ebay, I suppose. You'd probably have to discount the card a bit though!
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To be yourself in a world that is constantly trying to make you something else is the greatest accomplishment ~ {Ralph Waldo Emerson}