There aren't very many imaginary organ-griders in the literature.  The caption here reads, "Do you not perceive an Italian organ-grinder over there?" (English Illustrated, 1900).  In 1886, "Tom went to the window, called out to an imaginary organ grinder, pitched a copper, and ordered him to be off with his hideous music" (John Robertson, One of the People).  In 2007, one Harrison Forbes blogged about traveling with an imaginary organ grinder's monkey named Ivan.