Theres a Super Wal MArt on the 192 by Medievel times, and another further down towards St Cloud (on left) and yet another on John Youg and Sandlake (between I drive and the Florida Mall)
The closest one to the parks is the one on 192. However, they are building a new Super Walmart on Osceola Parkway right near the Turnpike. Looks like it will be open in the next few months.