They stopped running buses to the parks a few years ago, because people would park for free in the DTD lots. This would not allow parking for the stores at DTD. You can do a few things. If you are already over at DTD, you can walk over to SSR or take the water taxi, and take the MK bus from there. You can also take the water taxi to OKW, POR, or POFQ as well and take the bus from there.
Just to make you aware, SSR shares buses with the Treehouse Villas and POR/POFQ do share buses at busy times of the day, so you cannot always catch the first bus.
The last alternative is to take a DTD bus to any of the resorts on the monorail - Poly, GF or CR.