France issued this booklet of stamp featuring musical instruments in 2010. January 29 was the first day of issue, with the pane available to the public on February 1. The stamps bear images of artistic representation from a variety of artists. The organ stamp is from a work of art by Francois Garas, completed in 1896. The original artwork utilizes pencil, ink, pen, watercolor, pastel, paper. It hangs in the Musee d'Orsay. As a work of art, I am assuming the original does not depict an extant instrument, but rather the artist's interpretation of an organ. The stamp does not appear yet in my 2011 Scott catalog. I found reference to it here with information from the French philatelic catalog.
Here is the catalog information:
Yvert et Tellier B390
Here is an image of the original artwork: