Don't know anything that is not textbook like - you could try the Singapore Math Challenging Word Problems book (http://www.singaporemath.com/Challenging_Word_Prob_for_Primary_Mathematics_6_p/pmcwp6.htm)
or you could buy the "Key To" series (you can select the topics that your son needs to review - this is book 1, there are 10 books - https://www.amazon.com/Key-Algebra-Book-Operations-Integers/dp/1559530014 )