Junkyards is where most parts are picked up for those cars. If you need a part, post it up and someone might have one or have one near them.
As for performance parts that you suggest, custom is about all you'll be doing with them. CIA will have to be made, and modifying one made for another car seems to be the main way of doing it. Valve covers again will be custom, probably with you finding a set off another car, and cleaning/painting them yourself, or having someone do them for you. Not sure if they'll work on your year motor, but some later f-body 3.8L motors has aluminum valve covers which could be polished.
For the tail light lenses, you are pretty much stuck with stock, tinting them, or making your own.
Hope that helps. If you do your own custom stuff, take pictures and post them up.
2007 Saturn Aura XR | 1970 Chevy Blazer 4x4 | 1970 GMC 3/4 Suburban 4x4