You might try googling "square $COMPANY logo" or other similar things. ...
Yeah I had been having a rough time finding good ones with google, but I had much more luck once I started using google's advanced search settings to configure the type as "clip art", the aspect ratio as square, and the filetype as png.
I've had pretty good luck searching for company "icons" rather than "logos". I think that pretty much implies square, but I guess the resolution might not go up that high (I didn't really care that much about the resolution though).
Aurimas
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