www.oddball.com for socks. They have shoes, too, but the exchange might kill you right now. Last two pairs of size 15 shoes I bought were from
www.amazon.ca. Here are some size 15 Adidas shoes on Amazon maybe he'll like:
https://www.amazon.ca/gp/aw/d/B00JR4...didas+shoes+15.
Splurge on the socks, by the way. They will last a long time as they're great quality and he'll be so much more comfortable and look more normal in them.