Go to Treasury Bill, Note, and Bond Auction History
Board of Governors of the Federal Reserve and click on Economic Research and Data
Interest Rates - Federal Reserve Bank of St. Louis - FRED

Use Bloomberg, available in the Margolis Market Information Lab (MIL) at the Business Instructional Facility (BIF).
Press the GOVT key, type TK then press GO to find ticker symbols of securities issued by governments and government agencies from countries around the world.