For those above mentioned HJC helmets, I do not believe they are SA (Snell Automotive) approved rather SM (Snell Motorcycle). They have a specific section of their website devoted to AUTO and i believe those ones that specifically state the SA2005 are such.
http://www.hjc-motorsports.com/products.htm
I have also had good luck with the following website and have ordered from them.
http://www.apexperformance.net/cartgenie/prodList.asp?scat=274
use coupon code bimmerforum-10 to save 10%. found that googling their coupon codes.
I ordered the zamp fsa-1 helmet as a track helmet. I also hoped this could serve as a dual-purpose helmet for my bike as well. I am happy with it as an auto helmet but for bike use it has way to much wind noise for my prefference (creates a high pitch whistle). This makes it hard to find a dual purpose helmet without actually being able to take a test ride in one.
hope some of this information was of assistance