Where can I buy parts like this that will work on the iphone 4?

I want to switch out the graphics, internet receiver, 3G receiver, CPU, RAM and screen on my iphone 4 with parts that are much more powerful. Where do they sell these parts?

Try eBay or apple stores… Internet is generally your best place.

You will find out that swapping any parts voids your Apple warrantee. And odds are, you will destroy the phone.

The parts are made to play together, you can't just swap out one part for another, it won't work.

And, the parts are all surface mount devices soldered in place, you would find it very difficult, unless you have lots of experience, to remove a part without damaging the board.