Book  (Jan 2000)  Page(s) 230.  
 
Kokamon Tree Peony. ex Japan [no date given]... semi-double red

Website/Catalog  (1956)  Page(s) [1].  
 
Japanese Tree Peonies
Koka Mon (Gate of Koka) Large blackish crimson...$6.00

Article (magazine)  (Jan 1955)  Page(s) 58.  
 
Alphabetical Check List of Tree Peony Names In  Public Collections And/or Available in Nurseries 1954-1955
Japanese, Crimson, 'Koka-mon' (Gate of Koka) (Chug. 1932), [Nurseries] William Gratwick