There was a manual transmission option on the Monte Carlo in 1970 and 1971. I remember going to one of the NMCOA conventions in the early '90s. According to the owner, the car had the base powertrain in it, which was the 350 with the 2 barrel carburetor, and a 3 speed manual transmission on the steering column. He said he bought it from a farmer who bought it new, and thought it was a good setup for getting unstuck from snow or mud, because you could rock the car back & forth from 1st gear to reverse easily with the 3 speed column shifter.
GM offered a manual transmission again in 1978 and 1979. The V6 could be had with a 3 speed manual with floor shifter, and you could get the 305 V8 with a floor shifted 4 speed manual. The 4 speed cars are pretty rare.
Then, as mentioned above, GM built a 350/4 speed Monte SS for sale in Mexico in 1984. There was a member that was on both this site, and MonteSS.com, that imported one of the Mexican Monte SS cars into the States last year. The car was for sale in the States last year, after he had imported it. Not sure if he was able to get a clear U.S. title for the car though.