Location. ISO 690

If only a limited number of copies of an item are known to exist, “At:” should be given before the place name, qualified if necessary (see Production > Place > General), followed by the name of the repository that holds the cited copy and its call number (or other locator) in the form used by the repository. See also Specific categories of information resource > Electronic information resources or parts and contributions thereof > Availability and access and Specific categories of information resource > Graphic works > Location.

EXAMPLE
GOSSE, Sylvia (1881–1968). The Garden, Rowlandson House [etching and aquatint, 1912]. At: London: British Museum, Department of Prints and Drawings. Register number 1915-27-41.