Heres a great chance to build your own custom sidelock 12 bore shotgun! This is a Belgian made Britte bar action sidelock 12bore SxS barreled action. It has 27 5/8" dovetail lump construction barrels with a swamped rib. The action boasts reinforced action bar, bushed strikers with gas venting, a hidden third bite to accompany the double underlugs, intercepting safety sears, an articulating front trigger, southgate ejectors, and an anson pushrod forend release.
This project will certainly require a skilled individual to complete. It can be completed by me in my shop, or I can make several other professional recommendations if you should seek such help.