I've found about a dozen silver dollars, in my 37-ish years. Several after beach storms, some in old-town urban demolition sites, 1 in a turfed yard, etc....
But the guys with the most staggering totals are some of the early hunters from states like Montana, Idaho, and Nevada. I have heard that they circulated there the longest , as Argentium says. Right up to the discontinuance of silver in 1964-ish. Reason is, that those states were silver mining states. So there was some sort of laws to favor silver dollars, versus paper currency, so as to promote the silver mining industry. However, I can't find any web-links about this right now, so I'm not sure where this came from. Just saw someone else cite that as a fact from a similar thread years ago.
Therefore, some of the earliest hunters in Montana, Idaho, and Nevada, were known to have found dozens upon dozens of silver dollars with their early BFOs and TR's. Like, they could be found simply in any sandbox that dates to the '50s - or-earlier, with ease. Needless to say, I'm sure all the easy pickens were stripped from those easy-to-hit spots earlier on.
Still though, perhaps those states would, to this day, be the place to have the best luck at fumble-fingers silver dollars (versus caches or some other strange-reasons).