They are in Amdusias's chamber, on the ground. Head towards the blood alter and you should see them. Hide In Shadows may help, if you have it, or you could just run in and grab it as fast as you can. The dragon attacked me the first time I entered, but once the door was open a couple ghosts wander in; not sure if that was the cause, but I could walk in later to get the scales without being attacked, with Amdusias circling an area above, not paying attention to me.
