Onslows Auctioneers to sell rare postal and WWI posters Dec. 18 STOURPAINE, UK – On Dec. 18 Onslows Auctioneers will sell a rare collection of posters published by the GPO (General Post Office) between the 1930s and 1960s. These posters are duplicates of those that can be found in the British Postal Museum & Archive collection, housed in central London.