Nexon just distributed them for the PopTag! event. Check the DFO website under the Start Game button. Though a couple of people mentioned they didn't get theirs yet.
What did you get from your free keys? ;_;
I got... 2 timed Polkin's Head for M.Gunner and Mage, 100 Remy's touches, Canna's Pretzel, Canna's Flan, Kaleido Box.
I probably should had saved them for pets. :|