Flash :: Access A Stage Instance?

I'm using Flash CS5. I have some instances on my stage declared in the main class and I want to attach some events to them, however at the time of the main class constructor, these are declared as null.

What's the best practice for accessing stage instances? Is there an event listener I could add that will tell me when the stage instance properties have been populated?

Simple example:

public class bleepBloop extends MovieClip {
public var productName:TLFTextField;
public function bleepBloop() {
trace( productName ); // Here it is null
}
}

However, when I access productName later, it's defined.