Calendar cards are just what the name implies, cards that were sent out from many companies and institutions advertising their products and services. They were sent to potential customers each month, and was probably a costly enterprise for them back then. Many of them had holes pre-punched so they could be hung on a nail or hook. I don't know if anybody specializes in these cards but if they do it must be almost impossible to get a complete set of 12, and who knows how many years they put these out.
March-1906 April-1906 June-1906 July-1906 August-1906 September-1906 December-1906
THE CHARLES H. MOORE OIL CO.
January-1908 May-1908 July-1908
September-1914 March-1915 July-1916 August-1916
March-1917 July 1917 August-1917
THE STORRS-SCHAEFER CO. SPORTSMAN'S SHOT WORKS
August-1912 March-1914 March-1911 September-1911
THE R. A. KELLY CO. THE CALVERT ANILINE & CHEMICAL CO.
August-1912 May-1910 July-1910 October-1912 December-1912
D. H. BALDWIN & CO.
June-1906 August-1906 December-1906 January-1907
THE CHATFIELD & WOODS CO. THE MARMET COAL CO.
picture-same month-different companies.
THE TRIUMPH ELECTRIC C0.
WHITE RIVER CREAMERY CO.
February-1916 March-1916 August-1916
CAMPBELL COMMERCIAL SCHOOL
BARKER & FREISENS JEWELERS
FOR MORE CALENDAR CARDS