Re: materials sources?
What caliber? 223 or 308 and once-fired military brass is everywhere. 9.3x57mm Mauser will be harder to find (I know that from experience).
Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297
I always take precautions.
Beware the Evil Bullet Fairies.