We sell nearly all of the parts that make up the LongMill on our store page here: https://sienci.com/product-category/parts/. If you wish to build your own machine from scratch and require parts for your build, please check our store for parts.
We do not sell partial kits or make substitutions for kits. This is to keep prices down and ensure that we can provide warranty support for the kit as a whole. We recommend purchasing a complete kit as all of the components are designed to work together in harmony.