I see that the replies do not correspond with the section of Hand Ejectors 1896 to 1961 so, I suppose, any S&W "production" model would qualify (excluding experimental models that were never produced nor distributed)
The New Model 3 "Target" in .45 S&W Schofield. While there were not many New Model 3 (standard configuration) factory shipped in .45 S&W Schofield caliber either, (Ed Cornett had written an article in one of the Journals about the .45 S&W New Model 3s) there are only 2, known and verified, New Model 3 "Target" in .45 S&W Schofield Caliber. One is shown in Neal & Jinks book and I have the other as mine is a different serial number. I have not found, nor do I know of any others during my 30+ year quest to find same.
The .38 M&P 1905/4th change with Factory Chrome finish. Currently only 3 are physically accounted for but likely more out there somewhere. It is still unknown exactly how many were produced but most current research (and letter from S&W Historical Foundation) shows the 2, 6" 1905/4th chrome finish I own were shipped in a shipment of 35 total, as 30 (6") and 5 (4"), shipped in 1960 to a dealer in NY at a bargain clearance price of appx $10 each with mid 1930s serial numbers. The actual total produced could be anywhere from these 35 to possibly 200. Odd is that very few (less than 8) have been verified to exist. Only 3 are currently known to exist, with another 5 (approximately) which I think were all 4 or 5" barrels, have been mentioned by other members that have had past ownership or who had personal knowledge of same.
Originally manufactured in an attempt to find a replacement for nickel becoming scarce in the years leading up to WWII. Several went out for testing and all failed testing so never commercially released in chrome finish but at least 35 were placed in the vault at S&W and stayed there until 1960. Odd these were not shipped out and used during WWII but possibly the several that were tested and failed had something to do with NOT releasing them. Oh, no one knows what happened to the several that failed. It seems, as best that can be ascertained, the test revolvers all had the chrome peel from the cylinder during heavy testing. No known records of what happened to the test revolvers, either.
Pre and early post-war to Model of 1950, 44 Special Target with 4" barrel. 200 or less, if I recall correctly.
Also the Model 52A in .38AMU only 87 produced.