It’s been driving me nuts that Apple removed the Save As command from Pages and other Apple apps; a huge mistake in my opinion, particularly because I’m used to the idea of editing a file (say, a contract that I’m using for advertising) and doing a quick Save As; I *never* remember to duplicate ahead of time.
But I hadn’t bothered to Google it until today; and I immediately found a pleasing answer via TUAW. It turns out it’s not a Pages thing, but an OS thing (which makes sense) and the Save As command has been returned in 10.8 and higher; it’s just hidden.
Open the File menu in Pages, Numbers or another Apple app that’s missing the Save As menu and then press Option; the Duplicate command changes to a Save As command:

Works like a charm!