Being that you have a 3G, there isn't a lot o here yet to beneift you, so you won't get much for parts, but I am aware of some solid systems for the 3G.
Here's a link to RRE
http://www.roadraceengineering.com/3gintexh.htm (solid DSM vendor) that lists some of the 3G mods. Anything made buy a company such as Greddy, APEXi, HKS, ect ect for your car can also be had by several of our vendors on here like MAP, LSE, and DB.
You could also look into getting a custom exhaust made as well by any of those vendors listed, and prices may vary. If you don't want to ask in the forums, send them a PM.
And welcome to the site, it's nice to get a few more 3Gs on here.