I think the first company to make something like the Lionel SP smoke pellets (the ones after 1946) was K-Line. Unfortunately these were not chemically the same as the Lionel SP smoke pellets. The K-Line pellets kind of smelled like moth balls.
I have further information on the SP smoke pellets but I don't think I'm allowed to post that information here.
I think you are correct on the K-Line smoke pellets being the first produced after the Lionel smoke pellets. I bought some of them back in the late 1970s from my local hobby shop. Later I purchased a few more bottles at York in the early 2000s. They are hard to come by. Actually, I can't really nail the smell down as being like moth balls. The odor in my opinion is certainly not unpleasant; in fact I kind of like it.