Since evoCore is mainly developed by the b2evolution team the latest version is available as part of the b2evolution project.
You can get the latest version from the CVS server on SourceForge.net.
Browse the CVS server (web interface).
The meat of evoCore can be found in the /inc folder.
Because it evolves all the time, there is currently no packaged release of evoCore as a standalone framework.
You can, however, get a full working implementation as part of the b2evolution package.
