Here is a nice recent example of the World's Fair padlock.
This padlock had a high bid of $545 (Plus $10 Shipping).1904 St. Louis World's Fair - Commemorative Padlock
Excellent condition. The key supplied with the lock is not original. It is a re-cut key that does open the lock with patience. You will have to find a blank and have a proper key made."Louisiana Purchase Exposition" was the title of the 1904 St. Louis Missouri World's Fair. 3 5/8" high x 2 1/2" wide. 4 lever push key. - eBay (14 March 2012)