Searching for information on Native American people and cultures can be challenging because these materials are indexed under a variety of terms. Many library catalogs and databases still index materials under "Indians." If searching for mythology of Indigenous People of North or South America, using specific tribe names combined with mythology or folklore might give better results. The following terms are typically used to index materials about Native Americans:
Project Gutenberg contains many books on Mythology of the Americas which are downloadable in epub or Kindle formats, as well as readable online.
From California Digital Library