The only way to "find" them would be to stumble upon the private key that holds them.
The odds of this happening are so small that it is basically impossible to find them.
This is true, but some private keys are hashes of some popular phrases or even worse - of words (=brain wallet). Some of them are lost and some of them are long forgotten, because it was a popular way of setting a private key in those early bitcoin days, years ago!
Not all of them are lost or forgotten, some of them still undoubtly belong to the rightful owners, too. But it would be best for the owners to move them to some more secure wallets, as the best practices have changed considerably during all those years.
What I want to say, that it is still possible to stumble upon private keys being in the form of brain wallets and the original phrases long lost or forgotten.