Okay. Sorry I misunderstood.
But the answer isn't all that much different. Nickel is extremely uncommon on the K-38 Masterpiece. The SCSW 3d and 4th Editions actually say it is "rare." That means only a tiny percentage (low single digits) were finished that way. I'm not aware of any data that defines it any more closely than that. You'd look long and hard to find one for sale.
The picture is brighter on the SAO. These were in regular production from 1961 until 1978 (so, -2 and -3 only). Note: the SCSW says until 1982, but Roy told me they actually stopped in 1978. I've never seen any production numbers, but they are neither rare nor scarce, just less common. I stumbled on my first one a few years back at a gun show and bought it for an excellent price. 98% condition with original, numbered, Magna stocks. That sent me on a quest for a second one, and it only took me a couple months to find another one, ANIB. As I mentioned earlier, it is only a few serial numbers away from the first one and they both shipped in 1973. Eventually, I'd like to add an ANIB SAO -2 to my collection, but it is a low priority for me.
The one thing you need to be careful of with the SAO is that lots of standard Model 14s were converted to SAO. It just takes the removal of one part from the lockworks to do it. In addition, S&W used to sell kits to convert to the correct hammer, so some converted guns appear to be factory. Only a letter can confirm that it shipped as SAO.