There is an intro book to Balance Benders called "Balance Math and More - Level 1". Both are from The Critical Thinking Co. which also has a book called "Math Analogies" that he might like...

http://www.criticalthinking.com/

I'd also look at "Math Paths", "Number Circuits", and "Coin Clues" from Mindware. The latter two aren't exactly algebra, but a lot of critical/logical thinking...

http://www.mindware.com/Home/HomePage.aspx