Where would I be able to purchase one?
Interesting! I had heard of the 2 different silvers but didn't know what was used when. Thanks for the infoMake sure you get one from an 05 or 06 or late 04. The Wheel Color code for 2003 & 2004 models up to May is (Sterling Silver), after that the code is (ultra silver metallic WA8867). The color is close but Sterling cap won't match your Ultra Silver Met. wheels. Or you can buy a can of Duplicolor Ultra Silver Metallic Code WA8867 and paint it if it don't match.
The early Sterling silver paint is impossible to find for touchup.