The Yellow Pages. Yeah, I know, no one uses the yellow pages anymore. Yet while it may not seem very scientific, if you are targeting a specific geography and a specific industry, product, or service, the Yellow Pages may serve you well as a potential resource. There are both print and online versions. The print version works well if you are targeted a very specific geography. But don't be swayed by the size of the ads. Often, some of the very best companies do very little advertising.
The most important point is the listing. Beyond that, you will have to do further digging to fill in the details.