Would something like Marks and Spencer on-line be any good for you? The prices are the 'original' prices rather than the vastly overinflated prices they charge here, the choice is much wider, and I think M&S go up to a UK 24 (US 20?). Not sure of the styles though, but more than in store. They only charge ?15 for delivery to HK, so even if you get a couple of pieces the savings generally work out. If you do find something in store you like, you can try for fit, and then buy on-line?
ASOS.com also deliver for free to HK and go up to a UK 18 which I think is a US 14. But I know getting stuff on-line is risky is case it doesn't fit as you say (they do allow returns though, but a pain if you have to do so).
Just thought of this one too - Long Tall Sally -
http://www.longtallsally.com/delivery - that does larger shoe sizes, and I guess long torso tops etc. Again ?15 delivery charge.
Good luck!