I hope it’s clear to you that these samples are not designed to be used as tiles: as is evident in your picture, the pattern does not line up across tiles, and the material should not be used as you have it shown. I presume that’s why you want to know how to prevent a material from tiling.
There are basically two ways. First, you can import the image as an image rather than as a texture. That will bring it in as an image object, somewhat similar to a group–a single instance of the image that can be sized and handled without sticking to things.
Alternatively, if you bring it in as a texture (a material), you must paint it on an area that is bounded by edges–either paint it on a face that is exactly the desired size of the image or enclose such an area on part of a face by drawing lines around the area, bounding a new smaller face, which will keep the material from propagating and tiling. You can subsequently hide the bounding edges so they don’t show.
As to your question about bringing in hundreds of swatches at once, there is a Ruby plugin called MassMaterialImporter, which will convert a directory full of jpg image files into a directory full of SU skm files, which you can open as materials in SU. The only hitch is that the images are scaled in the textures at a standard size, and you may have to rescale it from inside the Materials editor in SU to suit your application.