The installation images can be found here. The ISO image can also be used to create an USB stick you can use to boot and install openmediavault. The Debian binary/source packages used to create the installation ISO image can be found here.
The package repository can be accessed via http://packages.openmediavault.org/public. The repository is signed with PGP key ID: 2EF35D13, Fingerprint 0F6B CC17 C26B FADC 27F2 2100 7E7A 6C59 2EF3 5D13.
The source code can be found here.