They aren't too rare. If you spent less time trolling people here and more time looking around, you could find out for yourself.
Certain makers specialized in heavier type fowling & pigeon guns, so obviously guns bearing their names will have 2 3/4" chambers over makers who's specialty was making light game guns.
My G.E. Lewis is from 1905, original 2 3/4" chambers, it's odd that it's proofed for 1 1/8 oz instead of the more common 1 1/4 oz. My guess it was made for a fella who specialized in wood pigeon & shore bird gunning. The action is profusely engraved with wood pigeons, plover and golden plover.
Lots of Greeners, Rossons, Lewis, Jeffrey, Wild, even Purdey's , etc out there with original 2 3/4" chambers.
What I would look for is 6&3/4lb to 7lb game gun with original 2&3/4inch chambers. Never seen much use to look for English fowlers when $600 Sterlingworth extractor with 30" barrels can do just as well for less money. When it comes to old game guns the English were unsurpassed with exception of certain French guns of same period.
