Don't know whether this is completely old stuff for readers of this forum, or if it has any place here at all, but this site

http://www.puzzlemaker.com

turned out to be a useful resource when my wife found herself trying to teach Latin to third graders (and up) in a charter school last year with no pre-existing textbook or workbook. I don't know what commercial strings may be attached but she was able to use it without being bothered by any.