I am not an "expert" in the history of Smith revolvers by an stretch of the imagination. However we do have some very knowledgeable folks so hopefully one of them can offer you what may be a more correct response.
I am going only from memory here, so I certainly could be wrong. In the old days, Smith made a model 15, a .38spc with adjustable sights, a K frame, usually in either 2" or 4" barrel configurations. They called that model the "Combat Master" if I am remembering correctly. I also think they came out with basically the same revolver chambered in 22lr. I think they also called it the "Combat Master".
So unless I am confused, I think that is the revolver you came across. I spent a long day on the range once, when the agency I was working for had several of these .22lr they were going to get rid of. They had used them as training aid in the years prior in teaching proper revolver shooting to folks that struggled a bit with .38 spc or .357 mag handguns.
They wanted to shoot up all the 22lr ammo they had on hand before getting rid of the revolvers and asked for volunteers. Most of us that showed up, shot until we had worn blisters on our trigger fingers, and then swapped to our weak hand to continue firing.
I thought it was an excellent weapon and it did remind me a lot of Smith K frame revolvers in the 38/357 chamberings with adjustable sights.
I do not think Smith offers that handgun any longer - but again I am not a true Smith historian as some of our members are for sure. If you are looking for a .22lr revolver, unless the price is excessive, I think you would enjoy it. Just my thoughts, hope they might help some.
Again I hope other members with more knowledge will offer their thoughts as well.
The Model 18 is indeed the 4" K Frame in .22LR with adjustable rear and ramp front sights. It was originally called the "Combat Masterpiece". As far as its worth, last fall I picked up an 18-2 (1963 vintage) in 98% condition, no box/papers/tools for $350 and felt it was a good deal. Its a sweet revolver!!
As in the situation "twoguns" alluded to, the Model 18 Combat Masterpiece was introduced as a .22 cal., adjustable-sighted, K-frame training or "understudy" handgun to Smith's Model 15 Combat Masterpiece (in .38 Spec.) and later the Model 19 Combat Magnum. All three of these handguns are absolutely identical except for the calibers.
I had a old 18 many moons ago and they are a great revolver. You want to have some fun with them. Go squirrel hunting with it. You will come home with a sack full for supper. One of many guns I regrett trading off in my youth. Good luck with yours.