You can find publishers web sites (and their online catalogs) using any good search engine.
Legal: There are four major legal publishing conglomerates: Thomson Reuters (includes West), Reed Elsivier (includes LexisNexis and Matthew Bender), Wolters Kluwer (includes Aspen and CCH) and Bloomberg (includes BNA). There are still a fair number of independents, but they are comparatively small.
If you are just looking for legal publisher Web sites, links are posted by FindLaw, CRIV and the Social Law Library. Or just use a good search engine. You can find a printed list of legal publishers, with addresses and phone numbers, at the end of Law Books in Print (Bowker).
Unsolicited Materials: Publishers often send unsolicited materials in the hopes that you will pay for them. Federal law says that the practice of sending "unordered merchandise" is illegal and authorizes you to treat the merchandise as a gift that you can choose to keep, sell or throw away (39 U.S.C. 3009). If you do this, you might want to send a letter to the publisher. Check out the Sample Letters posted by the AALL Committee on Relations with Information Vendors (CRIV).