The Kaja Wink Stamp Wing Eyeliner Stamp & Pen ($25) comes with two separate products. The liner stamp is double sided with a wing shape on each end. It's labeled right and left for each eye so you know which direction the wing should be applied.
The stamp itself is smaller than the other two options that I tried and has a slight curve to it. If you like your liner with a flicked-up end, this one is for you.