Did you snag a female or a male. DD can still be bred to it, but only if you got yourself a female. I'm right now goin through and tryin to get the last 6 of those trainers to have females of Miltank, Houndoom, and Tyranitar. It's takin FOREVER! Even though yours can't get DD it's still a perfectly good pokemon. Go w/this MS.
Tyranitar @Quick Claw
-Earthquake
-Crunch
-Aerial Ace
-Blizzard/Ice Beam
Crunch cause of STAB. AA for fighting. Earthquake cause it's good for 2v2 and 1v1. Blizzard if for 2v2 and Ice Beam if for 1v1. Good pokemon though. Very good pokemon.
Hope this was of some help!