Where can I get some of Amdusias' scales?

Where Amdusias is of course. He shed a whole pile of them in his room.

Hmm i cannot find dragon scales , there is nothing in his room , chest is already opened is it some bug or what ?

Ok, on the way to the blood alter (bridge of bones), there is green mist. That is the dragon scales.

Wear your best magic defense stuff when you run threw here. You cannot kill the dragon until you get the scales. Then run out of the room and read the book.

bring a lot of potions...

I had a lot of trouble with that too. I just chugged a potion every time it was up, but still took me 4 tries.

Actually you don't need to run back out of the room. You can read the book right there and the dragon will transform. 1 Hide in Shadows should be sufficient to run up.

Also, try standing on right (or left but not center) of the green mist and facing it to pick up the scale.

Thirdly, Amdusias seems to die relatively easily in melee combat, especially if you don't have a very high damage dealing ranged weapon.

when i played with ranger it was pretty hard to kill.. but with melee i killed him so easly.
thousand strikes skills helps a lot