Hi, ZD-
The URL for the Harry Fox Agency is http://www.harryfox.com. Their "Songfile" Website will give you some help. Note, however, that the agency has copyrights listed for many traditional songs that are in the public domain. If somebody affiliated with Harry Fox claims a copyright, Harry Fox will collect royalty fees for that affiliate until someboy proves the copyright claim invalid.
If there's a question about a particular song, ask about it here in the Forum (under General Music, not BS). If it's obviously a song written by a known person after 1923, you might as well pay the royalty fees.
Ruses are different for Europe, but this is how it is in the U.S. Don't know about Canada, Australia, and the rest of the world.
-Joe Offer-