Here are two online books of songs collected by the Federal Writers Project in Nebraska, titled Farmers' Alliance Songs of the 1890's and More Farmers' Alliance Songs of the 1890's:

http://www.lincolnlibraries.org/depts/hr/wpa/NM_pdf/Farmers1.pdf

Also take a look at:

http://www.lincolnlibraries.org/depts/hr/wpa/NM_pdf/Farmers2.pdf

Also one titled Cowboy Songs
http://www.lincolnlibraries.org/depts/HR/wpa/NM_pdf/Cowboys.pdf