If you're meaning Lactaid or equivalent lactose-free dairy milk, I don't think you can. A relative was able to get some at one of the All Star resorts several years ago, but a CM had to get it from the back (as in, it wasn't out in the cooler for guests to select), and they were told that it wasn't available in the parks. Things may have changed, but I've never personally seen it available in the parks.
Soy milk can be found in most table service restaurants upon request and at a few quick service locations. Many restaurants also have Tofutti or Rice Dream dairy-free ice cream as well.