I stumbled upon a 50 pages (!) long PDF file about the Corrington-Bukowski correspondence. It's called, "The John William Corrington & Charles Bukowski Correspondence: On Poetry and Writing" - edited by James R. Elkins.
It looks likes good stuff. Here's the link:
I also found a PDF called: "The Class of Bukowski: Engaging LaGuardia Working Class Students with the Novels of Charles Bukowski", by Carlos Hiraldo, professor in English. It's about how he uses Bukowski in his classes.
Here's the link: