Start with listing on the AAA website:
See the extensive listings of fellowship and support on the AAA website: http://www.americananthro.org/LearnAndTeach/Content.aspx?ItemNumber=1906
See also the internship resources on the AAA website: http://www.americananthro.org/LearnAndTeach/ResourceDetail.aspx?ItemNumber=12951
Information and announcements on fellowships, volunteering, and internships can be found on the websites of specific organizations of interest to anthropologists. Some of these are listed below, but there are many others for you to research.
Fulbright Scholar Program: http://www.cies.org/
Wenner-Gren Wadsworth International Fellowships: http://www.wennergren.org/programs/wadsworth-international-fellowships
Council on Foreign Relations International Affairs Fellowship: http://www.cfr.org/thinktank/fellowships/iaf.html
Ford Foundation International Fellowships: http://www.fordfoundation.org/about-us/special-initiatives/ifp
AAUW International Fellowships: http://www.aauw.org/what-we-do/educational-funding-and-awards/international-fellowships/
Wilson Center Fellowships: http://www.wilsoncenter.org/fellowships-grants
Rotary Peace Fellowships: https://www.rotary.org/en/peace-fellowships
Smithsonian Institution: https://www.smithsonianofi.com/internship-opportunities/
Additional General Resources
MoneyGeek (general background information on being an intern): https://www.moneygeek.com/careers/resources/internships/
GoodCall (check for their annual, data-driven list of best cities for summer internships): https://www.goodcall.com/data-center/