Yeah, that's the house paint color page.
I went to the local PPG store here and asked about auto paint hardener. I was met by "HUH???". I'm betting you'll get the same response as most PPG places just handle house paint.
What you need to do is go to an auto parts store that handles paint. Up here it's a Carquest place and they just deal with paint, and have PPG and other brands. They can do custom mixed in a spray can for you, as well as custom mixes in a can. If they've been around forever, they may actually have the info you need (current PPG code for Windsor Blue).
