I found one of these just walking down the street, near a gas station:
I keep it in my box of coins, a while back when I was a kid there was some friend of my dads who had some foreign coins and gave some to me and my siblings so I have all the ones I got, plus a chunk of copper I found near lake superior in minnesota(probably wasn't supposed to collect it but at age 10 i had no clue), just looked cool so I picked it up and kept it. It is the same shape as Lake Superior, aside from a little pointy piece broke off but I still have that piece as well. But yeah IDK what the chances of finding a chunk of copper on a great lake shore, actually shaped like the great lake itself are but I found one.