As is indicated by the category name, Non-Governmental Ogranizations do not involve governments of specific nations. They are international in terms of cooperation but membership is made up of individuals and sometimes nonprofit organizations in multiple nations, working together to address concerns around the globe. Examples of the many NGOs include Doctors Without Borders and Amnesty International.
Locating organizations of this nature can be done through publications like The Yearbook of International Organizations, published by Union of International Associations. Basic information can be obtained from the entry in the yearbook and additional details might be found on the ogranization website.