It's likely that it's a single stage. A good dealer can tell you for sure. Get multiple opinions if necessary - a lot of people will tell you that everything is cleared. I know of a couple other "lower"colors that were single stage in that year - 700 Alto Gray, which goes under 040 black and 199 black pearl, and 176 Shell Gray metallic which goes under 702 smoke silver. I would suspect that your's is also single stage. These are exceptions to the rule that metallics are always clearcoated. The lowers have a matte finish and look very strange and out of place with a glossy clear. If you really want to clear you need to use a satin finish.

I think you pretty much have to trust the paint store to match the color. Just find a good shop, or it sounds like you might already have one. You might take in a license plate bracket or something to help them along. If they can't find the lower color code that goes with your upper, a dealer parts counter can ususally help you. The lower code is not on the data plate and is often missing on the VMI. The parts guys are used to selling touch up paint for bumpers.

I absolutely would shoot the premium PPG - great paint - it would be a waste of time to search for anything else.