Following his death on 3 May 2010, obituaries and appreciations for Peter O'Donnell began to appear in a number of places, including the following:
Peter O'Donnell's official website: Modesty Blaise, Ltd.
The best place to start looking for Modesty Blaise information is The Modesty Blaise Homepage, which includes a wealth of data, including a reasonably comprehensive checklist of the newspaper strip stories.
Modesty artist Enric Badia Romero has his own page, showcasing his work on both Modesty Blaise and Axa.
Sussie's Modesty Blaise index contains more than you'd ever want to know about the newspaper strip. Unfortunately (for me) it's mostly in Swedish.
A good way to get in touch with Modesty fans from around the world would be to join the Modesty Blaise Online Fan Club.
Modesty Blaise and Peter O’Donnell and the Last Great Adventure Strip is an essay about the comic strip by R.C. Harvrey posted on The Comics Journal website.
The Once and Future Princess... is an extensive site with content in both English and German.
You can keep up with all things Modesty Blaise related at the Modesty Blaise News blog.
Ken Pierce Books is the publisher of the "First American Edition" series of newspaper strip reprints.
Rick Norwood is the publisher of Comics Revue and Modesty Blaise Quarterly, as well as a pair of trade paperback reprints.
Between 2004 and 2017, Titan Books published a series of 30 books reprinting the complete run of the comic strip in chronological order.
An influence on the concordance was Clark A. Brady's The Burrough's Cyclopædia: Characters, Places, Fauna, Flora, Technologies, Languages, Ideas and Terminologies Found in the Works of Edgar Rice Burroughs, a fascinating book published in 1996 by McFarland & Company, Inc., Publishers.
If youre searching for out of print books by Peter ODonnell (or anyone else, for that matter), you'll almost certainly find them at AbeBooks.com Happy hunting.
The Internet Movie Database has entries for the original 1966 film, the 1982 TV movie and 2002's My Name Is Modesty.
Wikipedia has this entry for Modesty Blaise.
The late Don Marksteins Toonpedia - an excellent reference for all things comic-related - has this overview of the newspaper strip.