iPhoto Picture Book larger than 28 x22cm - how do I specify?

A few years ago, I made an iPhoto book using the Picture Book theme that was larger than 28x22cm. Now, when I try to order a book, I am only able to choose within the Picture Book theme from the hard, soft and wire bound options, and I don't have any ability to change the size of the book. I'm ordering from NZ.

Does anyone know whether there is any way to buy a larger book using Picture Book? Does another theme give you that option?

Thanks so much!