Smith produced both commercial and military K & J frame revolvers with alloy cylinders, the first Airweight Chief Specials (Pre Model 37's, J frames) had alloy cylinders and are very much coveted by collectors, the switch to the steel cylinder was made in 1954. The SCSW indicates approx. 3777 were produced with the alloy cyinders with 609 going to the Air Force. The .38 M&P Airweight (pre-Model 12, K frame) was also produced commercially, and until 1954 with the alloy cylinder, I see these offered for sale, not all the time but they don't seem to be as rare as the early J frames, at least to me.
This week there was a C prefix SN pre-12 with alloy cylinder on Gunbroker, I don't know it it sold but it had its finish stripped from the cylinder and frame, the barrel was blued, kind of an interesting revolver. I only mention this as the photos were excellent, I'm not endorsing it nor do I have any connection to it.
I think Smith should re-introduce the Model 12 with upgraded alloys (and leave the IL off) - I have a 12-2 I like to carry, it is so very light, and I only shoot it with standard pressure loads. If the current alloy Smith's (637, 638, etc.) can stand +P I know they could make an updated Model 12 rated for +P and I think there would be a market for it, especially if it had a 3" tube.