Lots of parents—homeschooling ones or not—like to search for workbooks and other educational materials for their children. Personally I have had the most luck at the dollar store, but we don’t really use workbooks much.
That said, when my daughter was a baby, I did purchase a Hooked on Phonics Pre-K Super Workbook through our book club, and the other day she found it. Granted, she’s a bit too old for it now, but even so, she was incredibly bored with the book. Flipping through it, it was easy to understand why.