You can get dragon scales if you go inside the giant tree and make your way down and into the dragon cave. There are I think 3 or 4 you can find. You can also get them by beating the dragons that use lighting but it is a very rare drop.
Alright. So ultimately, I will end up with enough scales to upgrade _perhaps_ one weapon which requires them. Obviously it won't be the drake sword. Anyone want to suggest what weapon I should be keeping an eye out for, that will result in the most powerful option for spending my limited number of scales?