There are two places for Apple in Doha.
Virgin megastore and a stall at the royal plaza.
I think the Mac comes with a global warranty so you should be okay.
But then again, when have you ever had a problem with your Mac?
I had one of the first Imacs and it lasted 5 years with no problems. I have the new one and its been running for almost a 1.5 years without a hint of trouble.