Not that I love supporting Amazon, but onlymakerheels go up to size 15 in women's (13.5ish men's) in most styles. Their off shoot brand Vecipatcare seem to be in men's sizes going up to size 15 also.
Sexytag goes up to 15, but haven't been super impressed with their designs.
Wetkiss heeled combat boots go up to 13 in women's (size 11.5ish in men's).