MLA

Saarinen, Eero, 1910-1961. Thailand, Bangkok. Box 12, folder 203. undated. https://collections.library.yale.edu/catalog/10020359.

APA, 6th edition

Saarinen, Eero, 1910-1961. (["Box 12, folder 203"])(undated)[Thailand, Bangkok]. https://collections.library.yale.edu/catalog/10020359.