You can purchase these inexpensively from The Tire Rack. For my application of fitting E39 wheels to my E28, I paid about $4 per ring plus $12 shipping. Plus they can provide you with expert advice on any related questions you may have.
I just got another set from TireRack.. That is the best way to go. Get extras to save on shipping next time you need em. I just got 16 of them this time. I never seem to have enough.
Can someone post a pic of the metal ones they have (or a link to a pic). I bought some from a wheel company in Florida I found on Ebay. They are aluminum and almost paper thin. I was using them on my e32 with Mille Miglia wheels that have the e39 center bore and had a nasty 50-60 MPH shake that swapping back to OEM wheels has eliminated. New UCA and rotors.
I just want to see if the rings may be the problem, or if the tires are out of round (bought used), or if the wheels are bent (also used, but look OK).
I also have a shimmy with the style 5s and I KNOW it isnt the tires or rims. They are all straight and roadforce balanced. I am using the centering rings, but I dont think they are centering enough. Is there a thicker ring I wonder? What is the hub size difference?