Revolver side plates are individually hand fitted at the factory.
All S&W side plates are machined, not cast, then the side plate is custom hand fitted by a Master fitter at the factory.
In addition, when the frame is polished, the side plate is attached with special screws and the plate is polished along with the frame to insure it's perfectly level with the rest of the frame.
Chances of getting a fit with a replacement are LOW.
First, it's not likely to fit in place, since the plates are hand fitted, and it's purely a matter of blind luck buying another and having it drop in.
Second, since the plates are polished along with the frame, a different plate almost always fits ether too high, or too low.
Last, the "K frame has had minor changes over the years, and whatever plate you get very possible won't fit under any conditions.
Otherwise, trying to get one to fit on your own is a straight crap shoot. Chances are about 95% OR MORE that whatever plate you buy will NOT fit properly, if at all, and you will have wasted your money on a plate that's useless to you.
Sorry, this is one downside to revolvers.
Unlike autos, virtually every major part is hand fitted at the factory, and new parts do NOT "drop in", especially not side plates.
A better option, is to have S&W or a GOOD professional refinishing service re-polish the original side plate and polish the scratches out.
You'd be amazed at what S&W or a pro re-finisher can do with a scratched up gun.