Ditto on the craigslist search. As long as the backspacing is about 40mm and the center hole is the same size for the hub, they should fit fine. Also look on http://www.car-part.com
" onclick="window.open(this.href);return false; and you might find some close to you. Yes, the Vibe and Matrix are the only ones with the exact same wheels, 16"x 6-1/2", so if you need to replace just a couple, you will have to buy only Vibe or Matrix wheels. One thing to consider, the places on car-part.com also can ship their parts across the country. Prices for the wheels start at $25-30 each and up. Shipping would run probably $25-30+ each.
Corollas did have a few alloy wheels in the 16" size, but they are going to run $75-100 each plus shipping.
FWIW, I bought a set of 17" Vibe alloy wheels from two sellers on ebay for a grand total of $230 shipped. But it did take me a month to find them and buy all 4 wheels.
Here are some of the 16" alloys on ebay for $65 each shipped as long as you are in the US. It doesn't say they have all 4 so you might ask. If so, that is a good deal as long as it includes the center caps too.
http://www.ebay.com/itm/03-04-05-06-07- ... 93&vxp=mtr
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There are a few others on ebay for a bit more. If you just need a pair, maybe you could buy two now and get the other two later.