M&S definitely stock up to a UK size 10 in most of their shoe styles - I know because I wear them. Otherwise it's men's trainers from one of the sports shoes stores. I've also sometimes ordered online from landsend.com .
M&S is also good for hosiery. Haven't managed to find any anywhere else in the region that stretches further up than mid-thigh
For clothes, you can sometimes get lucky when trawling markets like Fa Yuen St or Stanley (even women's jeans with a 34" inseam), but IME it's usually more time efficient to trawl the back streets of Sham Shui Po for fabric I like and then either make it myself or take it to a dressmaker/ tailor.