You did not state what you mean by ethnic. Do you mean world-wide or ethnic within the U. S.? For Negro work songs, the Lomax site Lomax 1939 Click on Audio Subject, then go down the list and click on work songs. For comments and some text, in the first paragraph under the Search categories, click on field notes.
As well as on this site, American work songs, both Black and White, are given in Lomax and Lomax, 1941 (2000), Our Singing Country, which should be in your school library.
In the Lyrics Search at this site, you should be able to find songs from Scotland, Ireland and England. For Canadian work songs (with midis), see the Great Canadian Tunebook: Canada
I don't know of a good site for European or Latin American work songs; a number of sites have them but they are difficult to identify from title alone.