Yes....take the point.....old BSA underlever spares arent exactly jumping out the woodwork. I was talking generically for all older guns really and probably later models than early pattern BSA.
John Knibbs once had spares for one or 2 of the early pattern models and Surrey guns had a selection of peep sight and rearsights for some quite old specimens.
I turned up a peep for a BSA Club at flee market last year 15 quid.