I've checked every terrestrial auto parts store in the area for the proper touch-up paint for my car. Mine's 13U/WA891K, the silver/light gray. Contacted every GM dealership in the area.
Turns out the official paint from the GM dealerships is no longer made. I have a feeling this is the case for most Vibe colors, unless it's a color still used. And nothing from the aftermarket stores, though I have one more to check that a friend suggested.
So, what does that leave me? Using something that's similar but not exactly the same? Or perhaps some of the ones I've seen online from third party sellers, non-name brand paints that may or may not match. That's about it.