I would like to research companies that employ technical writers.
I’m not aware of any research tool that is organized in quite that way, to provide that answer. However, what I thought of was to look for job listings for technical writing positions and see what kinds of companies are hiring them. If you get specific company names, you can research the companies and see what other kind of people they employ. You also might get an idea from the job listings of what kinds of other people they are likely to employ.
I checked Google for technical writing professional associations. I found the International Association of Business Communicators, and they do have a job section: http://jobs.iabc.com/c/search_results.cfm?site_id=65. I also searched Google for technical writing job listings and found DICE technical writing listings at http://seeker.dice.com/jobsearch/results/US/Technical-Writing. They seem to be huge, so you could probably get a good sampling from this.
Another thing I thought of was to look at the government’s Occupational Outlook Handbook, because they usually talk about the kinds of organizations that employ a specific occupation, which would give you an idea of the other types of people who work there. Search for technical writers here http://www.bls.gov/ooh/media-and-communication/technical-writers.htm .
If none of this does it for you, you may want to look around on a couple of library research guides we have created — one on careers at http://library.uhd.edu/career and one on professional writing and technical communication at http://library.uhd.edu/pwtc. These may give you some other ideas of places to look.