In 1966, there were a few that were sold to the general public and became street/strip cars. Since they weren't very competitive in 1966, I think a lot of them were turned into street cars after the season. I know of two that were found in junk yards and are in the process or being restored. One is a FABO members car.
As far as finding D/Darts for sale, the first one that I bought I found in Hemmings Motor News. I was working at Chrysler at the time and a group of us chipped in and got the Priority Mail version. I found it listed in the Oct or Nov, 1998 issue. Called the guy that day and made the deal with him. That's the white one that's been at all the auctions since 2009.
I found Ted's car by making friends with both Al and his wife Carol while working at Chrysler. Told them that if they ever planned on selling it, that I'd like to buy it. Got the call for that one 2 months before I retired and 3 months before we moved to Florida. What's one more car? After determining that it had the original engine in it and it was the first one built, it was mine.
I bought Dana's car after corresponding with him seeking the story of his car for the D/Dart website. Somehow the conversation turned into the "since you know D/Darts, I'm thinking of selling my car and would I know anyone that would be interested in buying it"? DUH......I would be providing I could get it shipped from CA to FL reasonably. I regretted selling the first one that I bought and was happy when this one became available.
So yes, there are cars available. You just have to be in the right place at the right time. And be willing to pull the trigger at a moments notice.
As far as Dana's D/Dart goes, I'll be out in the garage later today trying to get the headers back on the car. Had to update the clutch to a 10 1/2" setup and modify the oil pan. That all required removing the engine and trans. I've been procrastinating putting it back together because it's a real pain in the arse working on it. It has a 360-380 HP Mopar Performance crate engine in it now. The original engine is long gone.