Stan, I did only one years ago to replace a missing piece on a Lefever forend tip. I'm not sure if the missing piece was originally horn or ebony, but the inlet in the wood was already present. All I had to do was cut and shape a small piece of ebony to fit the inlet, and left it a bit proud of the surface until after the epoxy set. A heavy rubber band was plenty to hold it until the epoxy set up, with masking tape on the surrounding wood. I dyed the epoxy with the black dye that Brownell's has for AccraGlas. Of course, ebony is an oily wood, so you need to clean the ebony surface with lacquer thinner or acetone immediately before gluing. My missing piece was about 1 1/4" long and had an elongated triangular shape that pointed toward the rear.
The ebony wood I used for that little project came from some black keys I took from an old junk player piano that a friend was scrapping. I also took a handful of the real ivory keys, and still have them somewhere. I've seen the nice inletting job you did on your percussion rifle lock, so a project like this should be a piece of cake for you.
