Q: But won't going to a larger size, say for example a G-cup, mean needing custom bras and custom clothing?

A: Quite probably. The garment industry in general and the bra industry in particular seem to have niche products. This doesn't really give comfort to the woman who is shopping in the typical store, however. With any luck, the garment and bra industries will start to clue in, thus meeting demand with supply. Certain geographic areas seem better at this than others (eg, the UK in general).