I buy them right from the manufacture in quantity. It has gotten harder to get the outers lately, since the major company that was doing them went under (Aleris) There is a smaller locally company doing them too, and I just buy as many as I can as they do runs. (Both soft lip and standard)

On the centers, it all depends on what you want? Most of the wheel companies out there will not sell components over the counter, but I mainly buy right from the guy making them again (or through him from another local wheel company he does casting and billet cnc ones)
Of course if you have a certain wheel in mind, you may not be able to get the centers to them. In that case it would be easier to just buy a set of the wheels and have the back spacing moved to what you want.

If you do get the outers and centers, the outers have to be warmed up before the centers go in, and make sure you have them in square of course. Best thing is to spin them to make sure the run-out is in check before welding them together too.


The ones I am running on my car.. This is a pic from when I got them, I have the front outers sitting near them too now Soon as I get the front end of the car together I can measure for backspacing and have them assembled.




I've got some 18" Boyds around (old style ones) and think they are near centered backspace