In addition to the outlet mall (I-4), there's a few options for buying sneakers/footwear in Disney Springs. Among them are: Under Armour, Fit2Run, Sanuk, and Havaianas.
On one visit, I neglected to pack sneakers, and I was able to buy a pair at UA for a very decent price. I don't know if they still offer it, but they gave me 10% AP discount at the time. I picked them because they were among the lowest priced ones, but they were excellent.