Aitch, you are asking the impossible - it's very likely (given what we observe in situations where there is literally 100 per cent exclusive, more or less, bf, and I don't mean Scandinavia, I mean places like the poorer parts of the developing world) that virtually all women will be able to breastfeed sufficiently well to assure the survival of their infants for at least the first few months (as long as the baby is born without problems of prematurity or serious disability effecting feeding and digestion). There is a spectrum, though, and some women will find it harder to do this, and some babies will grow less well. In extreme cases where the mother is unable to feed because of her own serious illness, other mothers step in or the baby is given animal milks or very early solids.
In the West we have the alternative of formula, and its ease of use and availabilty means it will be given in circumstances when its very use will undermine breastfeeding...to the extent it has to be used because breastfeeding is no longer an option. On top of this, our own maternity ward practices and our cultural expectations and habits work against breastfeeding.
I think it is, in fact, meaningless to say 'only x per cent of women are physically unable to breastfeed' because we are never just physical beings - our culture, our expectations, our emotions, our healthcare workers have just as profound an influence on whether or not we breastfeed for a day, a week, a month or whatever.