There is no comprehensive, detailed directory for CPAs, but there are a number of free nation-wide CPA look-ups, such as CPADirectory.com and the links in ABC Search Engine. If that doesn't work, you can see if the accountant is licensed in a state that posts an online lookup; links are posted by BRB Publications and SearchSystems.net. Alternatively, you can use the fee-based professional licensing databases on Lexis (ex. NJ has NJ;NJLIC), Accurint or another vendor. For other states, call the relevant Board of Accountancy/Licensing (e.g., 518-474-3836 in NY, 973-504-6380 in NJ).
Alternatively, you might try calling the American Institute of Certified Public Accountants (888-777-7077) to see if the person in question is a member.
To find professional publications by a CPA, search the databases discussed in the "Accounting" entry.
Ethics: The AICPA has its own Code of Professional Conduct. To find out if a CPA has been disciplined, contact the relevant state licensing board; the AICPA post links to State Boards of Accountancy.