Anyone know where I can purchase an Aluminum Intake Manifold or an aluminum valve cover??

as of right now there are none

Well, I want to purchase a nitrous system for my car, but i don't want to go with too high of a shot that i'll be testing the integrity of my intake manifold...any suggestions?

go with a direct port system...injects it right with the gas....safest form of nitrous system, and most effective, as long as you dont spray too much for the engine to handle

or just get an CAI, and install the fogger on the pipe if you worried about putting a hole in the plastic manifold

Hey man, the 2.3 is the same one as in the brand new focus, www.cb-e.com or it's maybe www.cp-e.com sells an intake manifold and a larger throttle body for the 2.3 Duratec.

right but the head is different from the mazda3 VS the focus duratec i recall so i dont think they are interchangable

i couldn't say for sure, every website I've been on that sells parts for the mazda3 categorizes them as duratec focus parts...ie draxas.com