The majority of Robert Bonfils paperback cover art was done for Greenleaf/Phoenix Press. This publisher started out in Evanston Illinois. When the publisher moved to San Diego California Mr. Bonfils moved too. There is no way of knowing how many covers he did for this company, as no records were kept. But it might be safe to say he did at least 1,000 covers. Other Chicago based companies he worked for were Merit Books; (division of Camerarts Publishing) and Newsstand Library. He also did covers for Playtime Books; (division of Neva Paperbacks), based in Las Vegas Nevada.
Below are links to the lines he worked for. Not all of the covers for Ember Library were done by Bonfils. But out of the 96 book run he did 93 covers. And of the 0008 books he did 18 of the 20. The third link shows a piece of original art I own, along with the book it was published for. Enjoy the site.