The book "Lion Hearts" is about Karski's era in Poland, and features a chapter about Karski and his photo is on the cover; this radio interview with author Harry Lew gives a good background about Karski and others who helped to save people during WWII. (Click on "Download audio" to listen to the interview with the author.)
The book is available in the US from Polonia Books in Chicago or online
A comic book about Karski published in Italy, created by by journalist Marco Rizzo and artist Lelio Bonaccorso, it's called "L'uomo che l' scopri Olocausto" (The Man Who Discovered the Holocaust) and is in Italian.
A play about Karski written by Georgetown professor Derek Goldman and Clark Young, starred Academy Award nominee David Strathairn as Karski in a world premier performance, directed by Goldman at Georgetown University on Karski's 100th birthday.
The play was performed in New York and Washington, DC during July 2015 to much acclaim, including this Washington Postarticle by Peter Marks
Another review of the play is by Masha Leon, with this article from Forward
An article about the play's New York performance in the Tablet Magazine by Gabriela Geselowitz