Hi,
If you can't locate it on your Mac, you re download from here.
http://support.apple.com/kb/DL1349
"The Mac OS X 10.6.6 Update is recommended for all users running Mac OS X Snow Leopard and includes general operating system fixes that enhance the stability, compatibility, and security of your Mac. *It also includes the Mac App Store*, the best way to discover and buy new apps for your Mac. The Mac App Store, a new application you'll find in the Dock, includes the following features:"
Carolyn 🙂