I’ve had requests for public domain Cajun or zydeco music. One comes from a documentary filmmaker, working on a project about Native Americans who live in the Louisiana wetlands. See The Sunrise People (video) for more about this project.
There’s no public domain music that I’m familiar with. That’s asking a musician to work for free or with the promise of future payment. Contact me or comment here if you have any ideas. Let’s see if we can’t work together to help out this budget-strapped filmmaker.