Not sure if this has been posted yet anywhere, but I couldn't find it in here. This is a link for the California Air Resource Board (C.A.R.B). Those are the sh$theads that tell us what we can't put on our cars. Anyways the website has an aftermarket parts database that you can search by CARB EO (Executive Order) number. Of note....there are no parts listed for 2006 Si that I have seen yet. Maybe it takes a while to get inputted in data base. I will research further. You can also obtain CARB EO numbers from manufacturers (say like the Greddy bolt on turbo kit) and plug them in their database.
http://www.arb.ca.gov/homepage.htm