First things first. Illustrator is not a very good tool for making catalogs. I suggest using InDesign for making catalogs. Using Illustrator for catalogs is going to be a huge pain for you and the press.
Having said that, the way to add pages in Illustrator is:
Go to File>Document Setup. Then add make the width of your document multiples of 8.5 (ie if you want three pages, then make your document width 25.5) then choose the Tile Full Pages radio button.
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