The thing is, there is a toggle in the accessories menu to select different socks that you own, but at a glance, I can't see how you actually acquire them. Unless I'm missing something, they're not with the shoes, nor are they with the leg accessories.
They are in the NBA Teams Store section At least I saw them there. But I guess they can be applied for the MyPARK only 'cuz it's a bit weird if I'll play for the Wolves in Lakers socks for example