Doug,
When I'm out and about in my travels I typically end up in "boutique" type gun stores. An example would be, tomorrow, I'm heading to Manchester, Vermont to visit family and enjoy a bit of shooting. Manchester is the world HQ for Orvis and they have a pretty decent amount of fine shotguns ranging in price from $2000-$200,000.
What Orvis doesn't have, is 2.5" ammo. They will gladly sell you a Belgian Browning Midas Grade for $50,000 or several LC Smiths, Purdeys, Holland & Holland and Parkers.
What these types of stores do seem to have is obscure brands of shotgun shells, albeit they are still 2.75".
I see a lot of Fiocchi, Eley, Sellier & Bellott and Golden Pheasant at these places. Are any of these European brands known to be gentler on old guns? Or do these places just enjoy selling you a $50,000 vintage shotgun and modern shells that will destroy it in a few weeks? Is it possible to identify a particular obscure brand of 2.75" shell and know, "that is a legitimate, low pressure target load"?
Also, I'm really shafted here in Illinois because when I hunt pheasant on state land I have to use non-toxic shot (e.g. bismuth). How on earth am I going to find 16 gauge low pressure, non-toxic shot in 2.5" shells?
Old guns are beautiful...yet annoying.