One "useful type of resource is a collection of diplomatic documents. These collections are published by a government entity, an independent organization, or an individual. For example, Swiss practice in foreign relations is documented in a publication entitled Diplomatische Dokumente der Schweiz, published by the Swiss National Commission for the Publication of Diplomatic Documents. The Commission has also created an online database of diplomatic documents ." (Hoffman, Marci, Rumsey, Mary: 2012)
Try a Google search for
the name of the country and using quotes
You may find collections of diplomatic documents for particular countries either in an online free database or on the foreign ministry website for the country of interest.
Diplomatic proposals submitted during the course of a diplomatic conference may be located by searching within the documents compiled for that particular diplomatic conference, where available.
There are several many historical sources. Some are shown below, but there are finding tools to help you locate others on the More Guidance page. Select the right resource for the time period of interest and the type of document that you need.