I believe those may actually be 19" wheels. I had stumbled upon a couple of photos of those wheels back in January (see below), and I had labeled the photos as 19-inch wheels since that's what the person who posted the photos indicated they were. I can't seem to recall where I had run across those, though. So, I have no idea on their availability. It looks like these photos were snapped at some US auto show, given the amber side marker on the headlight.
Not according to the catalog... 18" 15-spoke alloy wheels...The 15-spoke alloy wheel's progressive design is matched by the dynamic elegance of the A5. It adds an extra level of customization to your Audi.
And if you Google the wheel description you'll get headings like the following: 2009 Audi USA Pricing and Model Changes (22 Jul 2008) ... 18" 15-spoke wheel (with all-season tires) available for 2.0T and 3.2 A5.
Might just be an option that hasn't hit these shores yet...