If you shop at a MAC counter or store, register your name with them when you purchase something.
Additionally, you can log on to MACcosmetics.com, go to your Account, then hit Edit under Account Profile. This will take you to a screen where you will see the following message at the bottom of the page:
"Find out what's going on at a M·A·C store near you. To receive email about special events and services, please select a M·A·C stores below: "
Under the above message it has two drop-down boxes that let you pick a state and store.