Search for online communities for, or even web 1.0 news sites specifically targeted at, people within your target market. Doing a search for "insurance agent forum" instantly yields good results. Try similar searches with keywords like 'community', 'news', 'social network', 'blog'(s), etc. instead of 'forum'.

Use Google Adwords Keyword Tool ( https://adwords.google.com/select/KeywordToolExternal ) to research both keywords that would lead to your product, and keywords for searches members of your target market would be making. Find out which terms are most popular (and most competed for). Then use Compete.com's Keyword Destination tool ( http://searchanalytics.compete.com/ ) both to find additional communities of your target market, and to evaluate the actual relevancy of the keywords.

E-mail me if you'd like some detailed help; I'm happy to provide advice on any more specific questions you might have.