Some dealers when they bust up a proof set to get the cons worth slabbing will just toss the ones not worth slabbing or with problems into circulation.
i've found a few canadian pennies over the years. also some mexico stuff. recently found a couple mercury dimes, and a 64 washington. also find some wheats every now and then
Last week the vending machine at work spewed out a 1964 Washington quarter. Wound up with a 1946 Washington quarter in change from 7-11 a month or so ago.