An Executive Communication is a message sent to the Senate by the president or other executive branch official. Presidential veto messages are an example of an "Executive Communication."
You can search on Congress.gov back to the 100th Congress for Executive Communications (EC), Presidential Messages (PM), and Petitions & Memorials (POM) sent to the Senate.
Congress.gov provides access to Senate Executive Communications (EC), Presidential Messages (PM), and Petitions & Memorials (POM) from the 100th Congress (1987) to the present. You can conduct fielded searches by word or phrase, communication number, document number, congress, committee, type of document, or congressional record date. Searches can be narrowed by using the filters on the left side of the results page. For additional information about searching for Senate Executive Communications see, "About Exectutive Communications".
Executive communications are also listed by communication number in the Congressional Record, which is available online from 1989-present and in printed form for previous years. In addition, the online version of the Daily Digest (Congress.gov) provides a link to the Congressional Record page(s) which list that day's executive communications.
The document text accompanying Presidential Messages are often printed in the Congressional Record the day the communication is received, as is the text of many Petitions or Memorials. However, Executive Communications text is never included in the Congressional Record and can be very difficult to find. The actual documents are given to the Committee(s) listed in the communication record and generally are available only if either the respective Committee or the Executive Branch agency publishes them elsewhere.