National Parts Depot carries the GM 105-1498 Grey/White (NPD # C-8800-1) and the GM 105-1499 Black/Aqua (NPD # C-8800-2) Spray cans or you can go down to your dealership and see if they have the GM numbers above. My GM dealer ordered me a case of the 1499 for me.
http://npd.dirxion.com/Main.asp Page 28
You can also go to ebay and order if from the guy in the midwest who mixes it that MR70 mentioned earlier. I wanted to but the HAZMAT paperwork to ship it to me here in Hawaii was putting it way out of my price range.