Doug,
I have a 2003 Z06 with the spuncast Speedline OEM wheels. Bought a small bottle of $5 touchup paint from O'Reilly's Auto Parts. Had to call a few to find in stock. Duplicolor GM435, WA9789, Light Gray Metallic. The match is near perfect to my eyes. You can also get this mixed at Auto Paint Stores in larger quantities.
Even though this color was used by GM during the early '90s, none of the Chevy dealers had any. Walmart might carry this as well, but their paint dept is usually a mess.
Let me know if you have any questions. Would be glad to email you a picture of the bottle. Also, you can hop over to
www.duplicolor.com for some info..... maybe they sell direct.