It does seem to be a frustrating thing to search for.
a toyota site appears to give it a toyota part number of 16603-28020 which appears to cross reference to a Dayco part number of 89180
A search for either of those part numbers will return a bunch of sites that list compatible vehicles, and one site may list only matrix, or only tundra, or only lexus lexus or scion, but nobody lists an all inclusive list
https://shop.advanceautoparts.com/p/day ... Term=89180 specifically says the dayco one doesn't fit a Vibe, but gives the following dimensions
Bearing Inner Diameter 1: 10.3 mm
Bearing Inner Diameter 2: 10.3 mm
Components:Pulley
Flange:Yes
Flat: No
Max Belt Width: 07 Rib
Groove Quantity: 7
Number of Bearings: 2
Pulley Diameter: 4.528 in
Pulley Material: Steel
Pulley Type: Serpentine
Pulley Width: 1.182 in
Total Bearing Width: 26 mm
You said yours 5-6" so maybe this one is too small. If yours measures to be the same maybe it is compatible, but Vibes get no respect and they don't know its a fit.
If you buy from advanceautoparts, now or in the future, its worth it to order the stuff online, even if they have it in stock, because the website always offers a discount that's not available if you order in the store