Looking for spent bullet casings

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I have been putting together native American crafts and it has occurred to me that spent bullet casings would be good in a breast plat. I need to find lots of them to put into breast plates and chokers, do you know where I can find them inexpensive (or free)?I prefer the center fire ones as these will be easiest to drill out the center so that I can put the sinew through to hold them in place. Thanks in advance and walk in balance. I did post in Craig's list.