https://bulstack.com/2009/07/02/stamp-catalogue-kingdom-of-bulgaria-part-i-1908-1931/
Stamp Catalogue: Kingdom of Bulgaria part I (1908-1931) - BULstack
Jul 3, 2009 - A list of all regular and airmail postage stamps issued by the Kingdom of Bulgaria between 1908 and 1931. Click to view stamps or to learn about the subject.
kingdom of bulgariastamp cataloguepart