I wear size 14 shoes and size 16 boots, both in a wide, so yeah I get where you're coming from. Fortunately it seems guys around where I live have the same problem, so there's usually something in my size.
On a more serious note Lyth, if you're looking for US sized shoes that big, try New Balance, they tend to have that kind of stuff.
I looked up new balance, they didn't have anything I liked.
I've been desperately trying to find some high tops, those things are damn hard to find in my size.
I don't know what size 13 is, but I got a mate who is insanely tall (2 meters 10 cm) and has giant feet. He can only get Air Max and footwear for basketballers either ordered home through the local sportswear retailer or through specialty stores on the web, that might be worth looking into for you.