The deep or “invisible” Web consists of those resources that, while accessible over the Web, are not subjected to search engine indexing. Imagine the sites you have visited that have a search box on them. If the search retrieves Web pages, those are probably in Google or Bing. But if it’s returning directory listings or other information that comes from a database, it may not be.
I came across Complete Planet in a list of “alternative” search engines. You can search Complete Planet’s directory of databases for relevant matches or you can browse by topic. The “Law” category has over 1100 entries. It contains common sites, like Findlaw or Lawyer.com, but not necessarily a lot of high quality ones. The site may only be a demo for its deep web search owner, BrightPlanet, as most entries in the legal category haven’t been indexed since 2004, and a number of the ones I clicked were no longer there. However, it may be worth noting since it covers a wide variety of topic areas and might help you to identify a source, even if the directory entry is no longer there.