With a laptop, that isn't very practical. If the laptop is used as a desktop (sits in one place with possibly other peripherals) that might be more of an option.
If you google 'gateway laptop keyboard replacement' you should be able to find a site that will sell you a new replacement keyboard. In my experience with laptop keyboards, they usually just have two brackets where they are attached to the laptop itself so it wouldn't be very hard to replace yourself.
As far as replacement keys themselves, I think you will be hard pressed to find someone (aside from perhaps ebay) that will sell you individual keys.
Hope that helped!