Where I can buy dedicated video card for my laptop?

I have an ASUS G72 which it already come with nice gtx260.

However what happen if I need to upgrade my video cards in the future? I try research website but find none. Does that mean even I have dedicated video card but won't have any part for me to change?|||You are stuck with the graphics that are in your laptop.|||You probably can't buy one. The only laptop video cards I have seen can be bought with a laptop at Cyberpower, Inc. They custom build gaming laptops and desktops. Most laptops are built for work and school, not games. A gaming desktop is faster and cheaper than a laptop.|||You'll have to check the Asus website in the future for a compatible replacement. It all depends on what the video card manufacturers release for your laptop. You have a great video card right now, for a laptop.|||The video/graphics card is a chip set made into the mother board and not replaceable or upgradable.|||You can't change the graphics card in a laptop.