Dear Mr. Keller,
Thank you for posting your request on History Hub!
The Supreme Court’s official collections of photographs and portraits are maintained by their Office of the Curator. See their Historic Collections and Photographs pages for more information.
The Supreme Court Historical Society has low-to-medium resolution images of all the justices on their web page. The Library of Congress has a collection of Group portraits of U.S. Supreme Court Justices. At least some Supreme Court Justices have portraits at the National Portrait Gallery. The Oyez Project may also have material that you can use.
Photographs of varying genres and resolution are also available on Wikimedia Commons. See their Category:Supreme Court Justices of the United States page.
We hope this information is helpful.