The UNCA (United Nations Correspondents Association or U.N. Correspondents Association) was founded in New York City in 1948. It has over 250 members today. From its inception, UNCA worked to bring correspondents, members of diplomatic delegations and the Department of Public Information together by organizing press conferences, social functions, luncheons and an annual awards event. The relationship between the United Nations Correspondents Association, as the organization representing the United Nations press corps, and the Secretary-General is based on an agreement dated, September 16th, 1995 and embodied in the UNCA constitution.
Sources: http://unca.com/unca-history/ and
https://en.wikipedia.org/wiki/United_Nations_Correspondents_Association

Its flag is a UN blue horizontal flag with the emblem in inverted colors (http://i.imgur.com/FxvAc2G.jpg) in the middle, as seen here: http://gdb.voanews.com
(source: https://therearenosunglasses.wordpress.com)

For additional information go to UNCA (official website): http://unca.com/ 
Esteban Rivera, 4 October 2016