When I did a Google search of clothes for little people, I came upon a site that has a list of links. One of them was for lands end, another for Cinderella shoes (which come very small). The site is ksg dot org, so keep an eye out for it. Some of the links are broken but many of them still work.
There’s also learning to sew, but obviously not everyone has the time or inclination to do that. If you do, though, there’s a lot of clothing modification you can do with a hand sewing kit.