Complex sentence: The Royal Doulton Bunnykins have been in continuous production since 1939, at that time only 6 figurines were produced as all factories were closed for the duration of World War II and so these 6 figurines have become very rare.
Split into simpler sentences: The Royal Doulton Bunnykins have been in continuous production since 1939. At that time only six figurines were produced, as all factories were closed for the duration of World War II. These six figurines have become very rare.