How to Build a Huxley
The currently only documented Huxley is the RepRapPro Huxley. As it's open source, you can build it from your own supplies, without that kit, of course.
The eMAKER Huxley is essentially identical; the instructions can be found at the eMAKERshop site, along with listings for part sets for the Huxley (as well as other varieties).
The TechZone model is generally not recommended, as there are some issues with the design and few sources of support, but the instructions are still available in the Huxley area, and the parts files can still be found in the TechZone Huxley pages.
The GenX model has some interesting features, but it can only be obtained from its developers, SKB-Kiparis, its documentation is available only in Russian, and the design files have not been released to date.