I was in Tombstone about 15 years ago when the Tombstone Western Film Emporium or Festival or something like that was going on.
My buddy Billy and I were walking down the street and in front of us was a guy dressed up like "Josh Randall" (Steve McQueen in "Wanted Dead or Alive").
I mentioned to Billy that the gun looks like McQueen's gun. The dude in front of us heard me and stopped and turned around and said "It is McQueen's gun" and began to edjakate me on Hollywierd's selling off of props.
He let me examine the piece. It was a true 1892 Win in 44.40 chopped on both ends and included the holster and bandolier . He mentioned that at the Tombstone HS gym the "Emporium" sale had all sorts of Hollywierd guns for sale.
We followed him there and the first guy he introduced us to, had 2 of the 3 "Rifleman" guns. We talked and examined his wares and both were 20"+ Win 1892's with the loop lever and a crude screw to activate the trigger. My first thought was that the Mattel version I had as a kid did the job better with the pivoted metal piece that tripped the trigger.
He had documentation on the studio letter head and a letter with Chuck Conner's signature verifying that Win M1892 s/n XXXXXX was the one he used during the filming of the series.
The price then (circa 1999-2001) was under $2k a piece and while I could afford to buy one of the 2, it would have put a really big dent in my bank account, but. The trip back to Bisbee was quiet as I was torn between buying a really cool gun to shoot/show off and the investment factor vs the money as I had just lost my job.
That night I talked to my Dad (whom I was visiting). Over a couple glasses of Maker's, he convinced me not to buy one. As it turned out, I didn't and have regretted the decision ever since. When I flew home and told my SO, (a true Westerns fan), she jumped my shxx and I've never heard the end of it from her or my local buds who would have loved to shoot a gun as famous as that.
I always figured that I'd never keep the gun for more than 2 or 3 years and then sell it, but me and my bud's would have fun with it, have some bragging rights and enjoy it for a while. Then I would put it up for sale and find someone like me who wanted a famous Hollywierd gun make a little money on it and still leave me with some good memories.
Anyway to answer your question, the guns are out there. They were sold in the late 20th century by the studios/prop companies to garner income.
They have "documentation" from the studios and are traded at shows specializing in Western Film history.