Hammerman,
I read an older article about the Chinese hammer double, it came with both short barrels for CAS type shooting and they tested the same model with longer barrels for the article. I think they still make the longer barrel one, you'll just have to have it ordered special.
Also for the higher end market, I think Fausti makes one, if your making 5000 the cutoff something custom may be possible from the semi-custom gunsmith/shotgun manufacturers
A lot of the older "brand name" doubles (manufactured for the chain stores of the day) had fluid steel barrels that were often made to look Damascus to keep up appearances with the expensive guns. if you keep shopping around one is bound to turn up sooner or later, just repair parts for these guns is a "do it yourself" or have one patient gunsmith to repair them for you. fortunately most of them were made to hold up to several lifetimes of use, and many spent most of that lifetime behind the kitchen door or in a closet or guncabinet somewhere, still waiting to be used.
I shot a lot of black powder through a N.R. Davis and Sons hammer double, it had fluid barrels, but I stuck to loading some tame BP loads just to be on the safe side. the game I shot didn't seem to mind, and the clouds of smoke was nostalgic, and unique to the hunting experience.
