H&R made a single shot. I saw a new one last summer at
a gunshow for $200. It was from an estate sale, the seller
said it was made in the 1980s.
Savage "sort of" made a .357 magnum single shot.
It was the Model 24 combination gun. .357mag/20 gauge.
So it was either a single shot , or a double shot, depending
upon your point of view.