You can download release materials from the project download page. Since Postgres-XC version 1.0, release tarballs comes with HTML document and man files.
Postgres-XC is distributed under the PostgreSQL license. Copyright is here.
Postgres-XC 1.0.3 source tarball is available here.
Postgres-XC 1.1.0 source tarball is available here.
This is the latest version of Postgres-XC release. Source tarball for beta release is available here.
DBT-1 benchmark material for Postgres-XC is available here.
Overview of this material is available here.