My ds is 15, wears a size 14EEE, or in some brands, 15. I got his football cleats off Ebay, there are a lot of sellers who buy odd lots of large size shoes for dirt cheap and resell them. I got him a brand new pair of cleats, good quality that fit perfectly, for less than $30, shipping included. There is no way I could buy a pair locally for less than a few hundred.
One thing ds really misses is roller blades. I found a few sites online that sell large sizes, but his feet are really, really wide and odd shaped. I think we're going to have to get a custom pair made, ouch $.