UCSB has created a database of recordings from old Edison Cylinders from the late 1800's to early 1900's. Could be very useful for period pieces. I would think this is all public domain.

The link to the site is here.

Very interesting write up of the technology used to convert the cylinders. Check the Project info page.

You will have to wait until the Slashdot crowd gets through overloading the servers to get to the recordings. The search feature doesn't work at this time. A link to the Slashdot discussion is here