They are now. They didn’t used to be. 28GG and 28H are pretty common sizes now
I remember looking in my mum's Great Universal catalogue - perusing the lingerie section, I have no recollection of large sizes, nothing over DD.
although, because of the misconceptions about cup sizes (ie. Bigger letter means big boobs)
It is counterintuitive. Maybe they should categorise bras by volume - i.e. 23/500 - for 28 band and 500cc cup.
Most UK high street stores will have a “DD+” section which caters for smaller band/bigger cup sizes now.
Do they have much over G on the high st?
The attached picture of Abbi Secraa - she has a very large bust - I just wondered on the bra she is wearing. Is that a good design for a lady as big?