Thank you. I will check with Kebco .You might reach out to Kebco. I know they brought in some Verney-Carron imports with splinter forearms.
Since these are generally custom ordered and built, reasonable customizations are pretty easy for the most part.
Regarding sanding down the forearm, that isn't an easy or practical thing to do with many double rifles because of the latching mechanism in them.
To pay someone qualified like JJ outside of Tulsa, OK to do the work, you would probably be better off buying a more expensive rifle with this feature already on it if you don't custom order one.