There are any number of MBA programs where you would have a decent chance of admission with a 500 GMAT score. Obviously, they are not well-ranked schools. I recommend that you get a copy of a B-school guide like Barron's or Princeton Review (or use their websites) and search for schools based on average GMAT scores. You can then narrow your list based on location.
Hope this helps.
Co-Author of: MBA Admission for Smarties: The No-Nonsense Guide to Acceptance at Top Business Schools
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