The source code of LuaTeX (and LuajitTeX) is hosted at Fabrice Popineaus place at Supelec (France): here. The sources and binaries of MetaPost and MPlib can be found: there

The official releases of LuaTeX are available as tags in subversion (which is what is used for TeXlive). They have numbers made up of a major an minor number. In prints we render the minor number in two digits. The revision is indicated by a one digit number and there can be at most 9 revisions. So, a number 1.05.3 means: major version 1, minor version 5, revision 3. Internally TeX has then \luatexversion (a counter) with value 105 and \luatexrevision 3 (a token representing the character three).

We don't provide any support for the code that is pushed in the repositories, only for the official (yearly) TeXlive releases and intermediate patch releases. We do of course listen to bug reports of the latest release as well as the current TeXlive tag. If needed we will release a revision. Bug reports should always come with an simple plain TeX or ConTeXt example that exposes the bug.

The (experimental) binaries are compiled regularly and available for several platforms on the build farm. If you install the ConTeXt MkIV distribution for your platform the right binaries and some support files will end up on your computer.