The offer of bras at both ends of the bra sizing table is much smaller, however I have fished out some brands and shops that have something in bands 50 (110) and up.
As I have already written, bigger bands are stretchier than smaller bands, so you might want to try smaller band sizes than what the calculator tells you.
Bands 32-52 and cups B-K. Available at Figleaves. Pretty, and has a variety of styles (including maternity bra, a sports bra and even a strapless !). The image on the top features their Beautiful Betty set.
Ulla (German brand)
Bands till 54(120), Cups till EUR L (UK GG). Really bbeautiful but a bit more expensive bras.
Available at naturalcurves.co.uk , delicates.co.uk
Available at Bare Necessities (US) and figleaves (US and UK)
34-56 (75-130) and cups till British JJ.
Available at Figleaves.
Simple, practical designs that won´t win beauty contests. Till band size 54.
This is a new sister-brand of Panache that focuses on bigger band sizes. Bands 36-46, cups till HH. Till now the offer isn't very varied -- only unpadded full-cups; but as 2013 is third brand's first year, I am hoping that they will increase the size range and design options.
Has theoretically band sizes up to 58, but in this size there is usually just one model available that could qualify as a visual contraceptive. However the choice gets much better at slightly smaller band sizes. Cups go up to N.
Band size up to 56, cups till H. The model selection is not overwhelming, but the bras are non-expensive and non-ugly. And a reader assures us that the bras are very comfortable.
Cups till N, bands till 58. Mostly basic models, with some prettier items thrown in.
What you can do:
Write to bra producers, telling them you´d like more variety at the upper end of band size table. This is especially effective if they already produce large-ish brands (lets say they have band size 50, and you need a 54). Be specific, mention specific bra models and styles you´re interested in.
I´m sure this is not a complete list. If you know any other brand / store that carries bigger bands, let me know in the comments !