I have stayed at a few DVC resorts (BCV, Kidani, Jambo, SSR) and visited all but OKW. From my experience, SSR seems to have the largest selection of DVC merchandise. Other than OKW, it's the only other all-DVC resort. Plus, SSR is home to the sales center. My guess is that's why SSR seems to have a larger selection.
IIRC, Boardwalk also has a fairly decent selection of DVC merchandise.