A new OMV package repository has been established as failover. It is already enabled in OMV3, but you can use it in previous versions if you add
deb https://openmediavault.github.io/packages/ DISTRIBUTION main
to the file /etc/apt/sources.list.d/openmediavault.list. Replace DISTRIBUTION with the name of the OMV version, e.g. erasmus, sardaukar, …