Mark, I'd second Stallones' and PALUNC's nomination of the BSS. 30" barrels are the longest, but find one of those and put in choke tubes, you're good to go.

Don't know how much luck you'd have finding a long-nosed Bernardelli hammergun, but if you prefer modern guns with hammers, they're a good choice.

Or how about a Classic Lion from Fabarms? Don't know how easy it would be to find one, but they imported some with 30" barrels and choke tubes.