I have the 08 si and went to my buddies shop and theres nothing out for the 08 si Dam Got to wait to 09 to get stuff for 08 lol
Like ZOMG dat ish iz crazzzzeee nikkuh... ddam son like toatly nuttin out der for diz Si
obviously your new to this... let's break it down shall we?
06-08 Civic Si = THE SAME THING
anything you find for an 2006,2007 Civic Si, will work for your 2008 Si
there are a plethora of Headers, intakes, cat-back exhaust to choose from, you have a lot of research ahead of you, I suggest you start searching