Down here in olde Hampshire it seems to be much the same as in Derbyshire. I have four older side by sides with 2.5" chambers and so cannot fire the 2.75" / 70mm cartridges filled with steel shot. We are told 2.5" steel is being made, but none has arrived in the shops.
Also the left barrels of all of mine are Full choke or almost, so to have that one choke opened out costs £100 / $135 at Teagues.

Bismuth cartridges are staggeringly expensive (quadruple the price) and hard to find. A Scottish shoot day that is booked for November has become non-lead, so I shall have to take my modern gun, a 48 year old Nikko with the barrels the wrong way round.

On our local shoot we eat all that we shoot, so what we use to shoot them with is our problem, but this will change in a year or three.

The recent Gavin Gardiner auction [good guy!] had eleven consecutive lots of classic 12 bore British sidelocks offered for sale with reasonable estimates; only two sold!
I intend to sit tight for the moment and not spend ANY money until life becomes clearer. Europe is also looking at a lead ban so this may be the end of an era - we shall see...

Historic Bore