Computer Arabia is the authorized dealer in Qatar. They are located next to HBK near to Sword Signal (Bank Street).
Other option is Redington on C Ring Road. Take left from Muntzah Signal (as you are going towards airport road), enter into first service lane, after 200 meters you will find Redington.

contact no. 4455 1608 & 4455 1609. Saturday to Thursday
9:00 am - 8:00 Pm

Hope this will help.