I got my in.pro ones from eBay although they're the chrome mirror ones, not matte like the S3. It's been almost 2 years and I haven't had any issues. I live in VA and go to PA frequently so they've seen plenty of different weather types.
I'm not too positive, but I also think most people got their mirrors, wheather Hagus or in.pro, from eBay.
I see you can get some from overseas (most likely OEM for the S3) for a few benjamins and a kidney from
http://vagparts.com
