"Pear's Complaint" is from the anthology, FromTotems to Hip-Hop: A Multicultural Anthology of Poetry across the Americas, 1900-2002, edited by Ishmael Reed (New York: Thunder's Mouth Press, 2003).
You can find "Bladder Song" in A Book of Luminous Things: An Anthology of Poetry, edited by Czeslaw Milosz (New York: Harcourt, Brace and Company, 1996). Leonard Nathan died in 2007. You can get biographical information from his obituary on the San Francisco Chronicle website.
A good source for apple allusions is the Allusions — Cultural, Literary, Biblical, and Historical: A Thematic Dictionary.