Thanks for your interest in Head First SQL. The book is available at http://oreilly.com/catalog/9780596526849 and you preview the contents at http://oreilly.com/catalog/9780596526849/preview#preview.
The code magnet kit is just a set of magnetized strips with code printed on them, which you can use to practice along with the book. The code magnets probably wouldn't be any use to you without the book. Here's what the code magnets look like: