I have been doing that with Ross rifles regularly. Anyone with a mill or lathe with milling attachment and a dovetail router bit can do it. Dovetail the two pieces together to a tight fit in an inconspicuous area (under a band is best), glue it up and it'll be tough as nails. Getting wood to match perfectly is pretty well impossible, however, and the work can be time consuming. I charge $200 for a Ross fore end for example.