The tree is now public:
Instructions can be found here on how to download and compile from the source trees:
Just to point this out:
1) Don't use this in production.
2) Don't assume you can upgrade from it
3) While we haven't designed it to crash, this is compiling from a source tree so bugs are very likely (please report bugs to bugs.mysql.com)
The changeset that is likely to become the Alpha is "Cset 1.2384"