I took a dozen packs of these to the UK Games Expo and sold all but a couple of them. They were a last minute item that I added to a non-gaming stationery order simply to reach the free delivery price point. Here's the blurb about them:
These double-sided cards are the same size as a standard business card (85x55mm), they have been professionally printed on sturdy matt cardstock.
They can be bought from squarehex.co.uk and, for people who just want a pack of these and nothing else, they are also on ebay with cheaper UK postage.