Check out
car-part.com. You may get lucky and find a 2009-2010 2.4L Base Vibe in a junkyard near you.
If that doesn't warrant any luck, check out
GMPartsCenter.net. I actually bought 8 brand new 2.4L Base wheel covers a couple years ago to use on our winter wheels. It was actually cheaper to get a brand new wheel cover than it was to buy a used one on eBay. A brand new one was only about $35.00 which isn't bad at all IMO.
EDIT: FYI,
GMPartsCenter.net lists a brand new 2009-2010 2.4L Base 16" wheel cover (
#24100434) for $37.15 before shipping.