The Library of Congress has released a fantastic free tool / resource called the National Jukebox. We used one such recording (poorly) on the most recent episode of The Mezzanine. Per their webiste:
The Library of Congress presents the National Jukebox, which makes historical sound recordings available to the public free of charge. The Jukebox includes recordings from the extraordinary collections of the Library of Congress National Audio-Visual Conservation Center and other contributing libraries and archives. Recordings in the Jukebox were issued on record labels now owned by Sony Music Entertainment, which has granted the Library of Congress a gratis license to stream acoustical recordings.
At launch, the Jukebox includes more than 10,000 recordings made by the Victor Talking Machine Company between 1901 and 1925. Jukebox content will be increased regularly, with additional Victor recordings and acoustically recorded titles made by other Sony-owned U.S. labels, including Columbia, OKeh, and others.
The Library makes the sound recordings in the National Jukebox available pursuant to permission from the rightsholders. Under the Music Modernization Act, many of these recordings will begin entering into the public domain on January 1, 2022, when all recordings published prior to 1923 will enter the public domain and will be free to use and reuse. Recordings published between 1923 and 1946 are then protected for 100 years, and recordings published between 1947 and 1956 are protected for 110 years. In addition, some of the items in the Jukebox, such as the Victrola Book of the Opera, are currently in the public domain and free to use and reuse. Disc labels that are more than 95 years old are now in the public domain and are free to use and reuse. The Library presents more recent disc labels with permission or under fair use.
You can use their searchable database of public domain recordings by format, repository, label, date, genre, target audience, and more. It is an excellent source of relevant and unique recordings for free use in your current and future projects.