Through their blog, Microsoft claims that their Surface Pro 3 devices are selling out in their recently added, overseas markets. In parts of Australia, all models were sold out early in the first day (we can of course question how many is "some retailers" and how much stock each had). The company expects to have appropriate stock levels in a week or two.
Honestly, I never quite get these announcements of low stock. While it is better than having too much stock, and these releases might ease the nerves of shy investors, having too low stock is a problem, too. It is often a sign of something lacking: production, confidence, market insight, distribution, and so forth. It can tell an interesting story if these sales figures are immense, see the Nintendo Wii, but often it just raises a critical eyebrow. This is especially true if concrete figures are danced around.
I mean, if someone is at a store and looking for a Surface but none is available, do you really need to let them know that you intend to make more?