How can I get more home screens / app pages on my iPad?

You can't. For the time being (as of iOS 4), 11 pages is the maximum number of home screens / application screens allowed on the iPad.

If you find yourself running out of room, chances are you can solve your space problems by creating application folders to store multiple apps in.

If folders simply won't do it, there are jailbreak tweaks available that will allow you to bypass Apple's limit of 11 screens.