I got Hub rings from this place. They are made from Alcoa 6061t6 billet aluminum. They aren't cheap.

http://www.motorsport-tech.com/hub_rings.html

I used them when I put new wheels on my 2003 Grand Marquis. I got some plastic ones from the company I got the wheels from but they were crap. I don't think the plastic would hold up anyway.

On the other hand, I ordered weld racing wheels for my 1965 Coronet and Weld specifically says they are lug centric and should not be balanced using the cone most shops use. There is an adapter that uses the lug holes to center the wheel for balancing.