Here’s one:
http://www.sfgate.com/webdb/prop8/
Just choose the “Supports Prop 8” option and enter the city or zip code, and voilà. Unfortunately there’s no way to filter out individuals’ names, so you may have to do a bit of scrolling in order to find the names of businesses amongst all the names of individual contributors.
Also, if you want to visit the website of the “Human Rights Campaign”, they have a list of a number of businesses which contributed to “Yes on 8.” We could use this list in a “reverse boycott”:
http://www.hrc.org/news/11542.htm
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