The Association on American Indian Affairs (AAIA) provides repatriation assistance. See their guidebook on International Repatriation here. For legal strategies on protecting sacred sites this AAIA handbook from 2008 is helpful: Native Sacred Places Protection Legal Workshop.
The Society for California Archeology Native American Programs Committee’s Sourcebook on Cultural Resource Management, Archaeology, and Cultural Heritage Values for the Native American Communities of California (October 2005, Fifth Edition).
To learn about a human rights law framework please see the United Nations Declaration on the Rights of Indigenous Peoples and this conference report by Kristen Carpenter et.al. entitled “Implementing the United Nations Declaration on the Rights of Indigenous Peoples in the United States: A Call to Action for Inspired Advocacy in Indian Country” and published by the University of Colorado Law Review (March 6, 2020).
The Department of the Interior National Park Service hosts webinars on NAGPRA training. They also provide NAGPRA grants to Tribes and museums to aid repatriation efforts.
To stay up to date on all things law related follow the “Leading Blog on Legal Issues in Indian Country“: Turtle Talk.
The Tribal Law Blog from the University of New Mexico School of Law promotes indigenous self-determination by facilitating discussion of the internal law of the world’s indigenous nations.