Use the first link http://reprap.org/wiki/Kossel
Open the part you want. Pick 'RAW'. Save the page as 'Text Document'. It will be saved as an stl file.
Open the Stl in http://www.netfabb.com/download.php. Some of the files need repairing, others although they are OK, would be rejected by Shapeways, due to thin walls. This wall will need to be increased to the minimum wall thickness, in whatever software you are familiar with.