The only shotguns I know of with a detachable magazine are the ones from Saiga, Savage, and Mossberg, though I am sure there are a few others...Glenfield and Marlin are likely to have produced a detachable box magazine version...but I've not checked-I know Glenfield is no more, and Marlin is not producing shotguns at this time...well, except the doubles.
The Saiga is a semi-auto, while the Savage and Mossberg are both bolts. Of course, there are the conversion units available for many pump guns that use a detachable drum-style magazine, but they are extremely expensive, and don't add much to the capacity....
