Yeah, I imagine as time goes on and the value keeps moving up, its only going to get harder to find them. As with anything there are shady people that come crawling out of the shadows trying to cash in so you definitely have to be careful as well if you do come across someone selling and do some research on them. Just as @mejustandrew said though, why would anybody sell one? I would hoard it until the end of days, or until retirement!