Great Dragon Armor can be obtained from Anthropus Camps level 5 and higher. There are a total of four pieces that you will need to obtain before you have the complete set, the Dragon Helmet, the Dragon Claw Guards, the Dragon Body Armor and the Dragon Tail Guard. Your Great Dragon does not wear any of this armor until you have found the complete set. Once you have the complete set, you are allowed to research Aerial Combat in your Science Center and use your dragon to attack along with your troops. The armor will be equipped automatically when the full set is acquired.
A common tactic used to get the armor is to use "wave" attacks. This involves attacking the target wilderness with an army sufficient to kill all inhabiting anthropos, and timing attacks (usually ofone SSD or Spy) to land AFTER your first attack and BEFORE the anthropus respawn. Below is a screen shot of how to do the wave attack.
In this picture the first attack uses 6k LBM followed by 1k LBM. For this tactic to work, it is nesscery to send an adequate second wave. If the second wave is big enough every other attack needs just one unit. Side Note: If you use LBM as your 1st and 2nd waves and plan to use Spies or SSD for the after waves, you must make sure the 1st 2 waves have time to reach the destination. Spies and SSD are much quicker than LBM. How long does it take? The actual drop rates of the Great Dragon Armor pieces are not difficult to find at all, I found all four of my pieces from level 5 camps. I spent about two hours using the above method and found my all Great Dragon Armor. Generally, it only takes 1-2 hrs to get all the armor if using wave, but because the drops are random... it may take you longer.