I carry an old S&W K22 as a trapline pistol. It has the adjustable rear sight. I dropped it and broke off one side of the blade and need to replace it. Can I get just the blade to slide in or will I need a fuller assembly? It looks like just the blade part would slide out if screws were loosened.

does it look like this ? https://www.gunpartscorp.com/products/1654460

You will need a new rear sight blade, windage screw, and retaining nut, Brownells and Midway both sell them. You have to break the old screw to get the sight blade out thus the need for a replacement screw. It is a fairly straight forward process as long as you follow the order of work, the only thing is to be sure and get the same size rear sight replacement blade. After you get everything put back to together you need to stake the retaining nut, they sell a tool to do this but you can do it with a phillips head screwdriver as well. If you have questions give me a shout.

Yes Pete that’s it. Thanks K9, I guess we’re neighbors.

Yes,there is a spanner tool to hold the nut on the left side as you remove the windage screw from the right.You need to realize,there is a very tiny detent,with a VERY tiny spring,on the side of that windage screw head.You better know what you are doing when you remove that screw or that tiny spring will fly into space.It is about the diameter of a pencil lead and maybe 1/8" long.

You also need to know there were changes made to the front of the sight tang,rounded or square.There are different spacing to the screw holes that hold the sight to the frame.I think the blades may still work in different sight bodies,but you better well study up before attempting to replace a blade.I use a spanner screw driver bit for the nut,the correct blade for the screw head,and a staking tool for the end of the screw.

You tighten the screw and nut till slightly snug,no play,then back the spanner nut out about 1/4 to 1/2 turn less,then stake the screw end.This keeps it from coming apart.Remember,while doing this,you have to keep the detent an it's spring in the sight body and the hole on the side of the windage screw head.If you have 3 hands you should be OK.
I often do this work in a gallon,clear bag in case the detent or spring come out.

Honestly,if I ever dropped a K22, and I promise you,I never will,I would have a pro check it out.Those fine revolvers are tuned like a fine Swiss watch and that is why they are so accurate.A slight bend in a the yoke,crane or ejector rod can cause serious problems.Besides that,replacing a rear sight blade should be done by a gunsmith.Replacing the full,rear sight,if you are careful to get the right one,is doable for a non-gunsmith type.

The other thing I would suggest is to figure how this happened and make sure it doesn't happen again.I think some of these problems are caused by cheap holsters.It is a dangerous thing to drop any firearm and I hope you keep yourself safe as well as that wonderful,S+W K22.

If I could suggest, if you have all the pieces yet, a competent Oxy Acetylene welder could join them. Yes it would need filing from you and then bluing, but you would have the original part. I have rebuilt a few firearms with broken pieces and there is satisfaction in the original and I enjoy doing it.