OAS official documents published since 2000 (there are a few older items) can be searched on the OAS Document Search interface. Specific types of documents can be found on the following pages:
The Van Pelt Library has collected publications from different bodies of the Organization of American States and also documents from its predecessor, the Pan American Union. In Franklin, there a number of possible searches:
"Organization of American States" as author/creator
"Columbus Memorial Library" as author/creator
"Pan American Union. General Legal Division" as author/creator
"Organization of American States. General Secretariat" as author/creator
"Inter-American Juridical Committee" as author/creator
"Inter-American Economic and Social Council" as author/creator
"Inter-American Commission on Human Rights" as author/creator
"Pan American Union. Dept. of Social Affairs" as author/creator
"Inter-American Statistical Institute" as author/creator
"Pan American Union" as author/creator
"Pan American Union. Division of Intellectual Cooperation" as author/creator
"Organization of American States" as a subject heading keyword
"Pan American Union" as a subject heading keyword
The Biddle Law Library also has documents related to the Organization of American States, which can be found through the LOLA Catalog:
"Organization of American States" as author
"Pan American Union" as author
"Organization of American States" as a subject heading
Use WorldCat to find OAS publications and books about the OAS that are held in libraries around the world, including the OAS Columbus Library in Washington, DC.
The OAS has a complex system of classification of documents, that includes a common designation (OEA), followed by a subseries (A-Z, with some letters still unassigned), and further by Roman numerals and then Arabic figures.
The series are as follow:
For updated information on the series, see Manual for OAS Proofreaders.
For detailed information on the subdivisions of each series, see Official records series of the Organization of American States: guide, outline, and expanded tables. (does not include information on Series N-W)
The Classification manual for the OAS official series, available at the Van Pelt Library in both Spanish and English, might also be useful.
Wikipedia: Leo Stanton Rowe, Professor of Poltical Science, U. Pennsylvania, 1896-1917; Director General, Pan-American Union, 1920-1946.