How can a decision maker identify strategic factors in the
corporation's external international environment?

Strategic factors being those things which will
impact you?  Or those things which you can alter?

Are you only interested in factors outside of the
country where the HQ are?

I'd advise you to check the GA Pricing Policy, but
will give you a couple of tips.

A simple structure might be a variant of the
Porters Model, and make five top level lists:

Government Actions & Economic Issues
Supplier Issues
Consumer/Customer Issues (all the way down to final user)
Competitor Issues, include potential competitors (substitutes)
Internal Issues

This could be a start, good luck!