The grand old firm of WW Greener has started making double rifles once again and claim that their Facile Princeps action is, weight for weight, the strongest in the world. http://www.wwgreener.com/

There is also a Russian firm that makes somewhat unusual double rifles that are really fine with hinged front triggers and gold plated parts - a member at another forum gave me the website though I saw an O/U rifle in Russia when I lived there many years ago. http://www.shipunov.com/eng/str/hunt/hunt1.htm

Good hunting!